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A    SHORT    MANUAL 

OF 

ANALYTICAL     CHEMISTRY. 


A   SHORT   MANUAL 


OF 


ANALYTICAL     CHEMISTRY 

<$aaliiaUbe  mitt  <$uanpftfaititt — Jnorpuic  antr 


BY 

JOHN    MUTER,    Ph.D.,  F.R.S.E.,  F.I.C.,  F.C.S. 

ANALYST  TO   THE    METROPOLITAN    ASYLUMS    BOARD  ; 

PUBLIC   ANALYST    FOR   THE    METROPOLITAN    BOROUGHS    OF    LAMBETH   AND   WANDSWORTH, 

AND    THE   ADMINISTRATIVE    COUNTY   OF    LINDSEY,    LINCOLNSHIRE; 

PAST   PRESIDENT   OF   THE   SOCIETY   OF   PUBLIC   ANALYSTS; 

LATE    EDITOR    OF    "THE    ANALYST," 

ETC.,    ETC. 


FOURTH    AMERICAN    EDITION— ILLUSTRATED. 

THE  CHAPTERS  RELATING  TO  THE  ANALYSIS  OF  DRUGS 
BEING  BASED  UPON  THE  EIGHTH  REVISION  (1905) 
OF  THE  UNITED  STATES  PH  ARM  ACOPCE  I A 


PHILADELPHIA: 
P.     BLAKISTON'S     SON     &     CO., 

1012,     WALNUT     STREET, 
1906. 


*  Authority  to  use  for  comment  the  '  Pharmacopoeia  of  the 
United  States  of  America,'  Eighth  Decennial  Revision,  in 
this  volume,  has  been  granted  by  the  Board  of  Trustees 
of  the  United  States  Pharmacopoeia!  Convention,  which 
Board  of  Trustees  is  in  noway  responsible  for  the  accuracy 
of  any  translation  of  the  official  weights  and  measures  or 
for  any  statements  as  to  strength  of  official  preparations." 


M39 
!90& 


PREFACE 
TO   THE    FOURTH    AMERICAN    EDITION. 


THE  continued  favour  with  which  the  book  has  been  received  has  encouraged 
me  to  persevere  in  offering  to  students  a  concise,  and  consequently  low- 
priced,  manual,  designed  to  introduce  them  to  the  chief  developments  of 
analytical  chemistry,  from  the  simplest  operations  upwards,  and  including 
many  organic  questions  generally  overlooked  in  initiatory  books.  By  working 
through  it,  a  student  will  become  familiar  with  a  great  variety  of  processes, 
and  will  then  be  in  a  position  to  use,  with  satisfaction,  the  more  exhaustive 
treatises  dealing  with  any  special  branch  he  may  desire  to  follow.  Originally 
written  for  the  use  of  pharmaceutical  students,  it  has,  I  hope,  far  passed 
its  primary  limits,  while  at  the  same  time  not  losing  its  value  to  them.' 
In  the  chapters  on  Volumetric  and  Drug  Analysis,  wherever  British  processes 
are  different  from  those  of  the  U.S. P.,  they  have  been  altered  to  suit  that 
excellent  and  carefully  compiled  authority.  Certain  comparatively  unim- 
portant matters  contained  in  the  ninth  British  edition  have  been  dropped 
out  to  make  room  for  the  greatly  extended  chapter  on  Drug  Analysis, 
necessitated  to  meet  American  requirements  as  contained  in  the  revised 
U.S. P.  of  September  ist,  1905,  but  even  then  it  has  been  found  imperative 
to  increase  the  size  of  the  book. 

J.U. 

SOUTH  LONDON  SCHOOL  OF  PHARMACY, 
325,  KENNIXGTON  ROAD,  LONDON,  S.E. 
DECEMBER  1905. 


TABLE    OF    CONTENTS. 


PART    I.— QUALITATIVE    ANALYSIS. 


CHAPTER    I. 
The  Processes  Employed  by  Practical  Chemists. 


8.  Solution 

2.  Lixiviati 

3.  Precipitation 

4.  Decantation 

5.  Filtration 

6.  Distillation 

7.  Sublimation 


PACE 

. 

I 

and  Extraction 

i 

a 

. 

2 

1 

.         . 

. 

3 

L              • 

4 

8.  Fusion          .....  4 

9.  Evaporation          ...  5 
10.  Crystallisation  and  Dialysis  .  5 
n.  Electrolysis  ....  6 

12.  Pyrology       ....  7 

13.  Preparation   of  sulphuretted  by 

drogen              ...  9 


CHAPTER    II. 
Detection  of  the  Metals. 


Group  Reagents         . 

.    10-11 

Division  A.              * 

.  18-21 

I.   Iron        .         . 

18 

GROUP  I.  . 

.  11-13 

2.  Cerium  . 

20 

I.  Silver      . 
2.  Mercurosum 

ii 

12 

3.   Aluminium     . 
4.  Chromium 

2O 
21 

3.  Lead 

12 

Division  B. 

.    21-24 

GROUP  II. 

.    13-18 

i.  Manganese 

21 

Division  A.    . 

I3~I5 

2.   Zinc 

22 

AT 

T  ") 

2'2 

i.  Aiercuncum 

4.   Cobalt    . 

23 

•                  14 

GROUP  IV. 

.  24-26 

4.  Cadmium        • 

I  C 

24 

Division  B.     . 

•                •                *  J 

.  15-18 

2.   Strontium 
3.  Calcium 

25 

25 

15 

_/•     _o 

2.  Antimony 
3.  Tin 

16 

I? 

i.   Magnesium     . 

26 

4.  Gold 
5.   Platinum         . 

17 

18 

2.   Lithium  .         . 
3.   Potassium 
4.  Sodium  .         . 

26 

27 
27 

<;.   Ammonium    . 

27 

Vlll 


TABLE   OF  CONTENTS. 


CHAPTER   III. 
Detection  and  Separation  of  Acid  Radicals. 


1.  Hydrofluoric  Acid  and  Fluorides 

2.  Chlorine,  Hydrochloric  Acid,  and 

Chlorides     .... 

3.  Hypochlorites      .... 

4.  Chlorates 

5.  Perchlorates          .... 

6.  Bromine,  Hydrobromic  Acid,  and 

Bromides      .... 

7.  Hypobromites      .... 

8.  Bromates 

9.  Iodine,  Hydriodic  Acid,  and  Io- 

dides     

10.  lodates 

11.  Periodates 

12.  Water  and  Hydrates    . 

13.  Oxides          ...*.. 

14.  Sulphur,    Hydrosulphuric    Acid, 

and  Sulphides 

15.  Thiosulphates  (Hyposulphites)     . 

16.  Sulphurous  Acid  and  Sulphites    . 

17.  Sulphuric  Acid  and  Sulphates 

1 8.  Carbon,  Carbonic  Acid,  and  Car- 

bonates        .... 

19.  Boric  Acid  and  Borates        ; 

20.  Silicic  Acid  and  Silicates     .         . 

21.  Hydrofluosilicic  Acid  . 

22.  Nitrous  Acid  and  Nitrites    . 

23.  Nitric  Acid  and  Nitrates 

24.  Cyanogen,      Hydrocyanic     Acid, 

and  Cyanides 

25.  Cyanic  Acid  and  Cyanates,  Cyan- 

uric  Acid,  and  Fulminic  Acid 

26.  Thiocyanates  (Sulphocyanates)    . 

27.  Ferrocyanides      .... 

28.  Ferricyanides       .... 

29.  Hypophosphites  .... 

30.  Phosphorous  Acid  and  Phosphites 

31.  Meta-  and  Pyro-Phosphoric  Acids 

32.  Orthophosphoric  Acid  (B.P.)  and 

Orthophosphates  . 

33.  Arsenious  Acid  and  Arsenites 

34.  Arsenic  Acid  and  Arseniates 

35.  Manganates          .... 

36.  Permanganates 

37.  Chromic  Acid  and  Chromates 

38.  Stannic  Acid  and  Stannates 

39.  Antimonic  Acid  .... 

40.  Formic  Acid  and  Formates 

41.  Acetic  Acid  and  Acetates    . 

42.  Valerianic  Acid  and  Valerianates 

43.  Sulphovinates  (Ethyl  Sulphates)  . 

44.  Stearic  Acid  and  Stearates  . 

45.  Oleic  Acid  and  Oleates 

46.  Lactic  Acid  and  Lactates     . 

47.  Oxalic  Acid  and  Oxalates    . 

48.  Succinic  Acid  and  Succinates 

49.  Malic  Acid  and  Malates 

50.  Tartaric  Acid  and  Tartrates          . 

51.  Citric  Acid  and  Citrates 

52.  Meconic  Acid  and  Meconates 

53.  Carbolic  Acid  and  Carbolates 


PAGE 

29 

54- 

55- 

29 

56. 

30 

57- 

3° 

30 

58. 

59- 

3° 

60. 

61. 

31 

62. 

31 

63- 

32 

32 

64. 

32 

33 

65. 

33 

66. 

34 

35 

67. 

35 

68. 

36 

69. 

37 

37 

70. 

38 

71. 

39 

72. 

40 

4i 

73- 

JJ 

74- 

42 

42 

43 

43 

75- 

43 

76. 

44 

45 

77- 

45 

45 

78. 

45 

46 

79- 

46 

46 

80. 

47 
47 

81. 

47 
48 

82. 

48 

48 

83 

48 

84. 

49 

49 

85. 

49 

5° 

86. 

Benzoic  Acid  and  Benzoates         .         51 

Salicylic  Acids     ....         52 

Tannic,  Gallic,  &  Pyrogallic  Acids         52 

Separation     of     Chlorates     and 

Chlorides  53 

Detection  of  Chlorides  in  Bromides         53 

Detection  of  Bromides  in  Iodides         53 

Detection  of  Chlorides  in  Iodides         53 

Separation  of  Iodide  from  a  Bro- 
mide and  Chloride  .  .  53 

Detection  of  lodate  in  Iodide       .         54 

Detection  of  Sulphide  in  presence 

of  Sulphite  and  Sulphate      .         54. 

Separation  of  Thiosulphates  from 

Sulphides     ....         54 

Separation  of  Sulphides,  Sul- 
phites, and  Sulphates  .  .  54 

Separation    of    Silica    from    all 

other  Acids ....         54 

Detection  of  Nitrites  in  Nitrates  .         55 

Detection  of  free  Nitric  Acid  in 

the  presence  of  a  Nitrate   .         55 

Detection    of   a    Nitrate   in   the 

presence  of  an  Iodide          .         55 

Separation  of  Chlorides,  Bromides, 

and  Iodides  from  Nitrates    .         55 

Separation     of     Cyanides     from 

Chlorides  55 

Separation  of  Ferro-  from  Ferri- 

Cyanides       ....         56 

Detection  of  Cyanides  in  the 
presence  of  Ferro-  and  Ferri- 
Cyanides  ....  56 

Detection  of  a  Phosphate  in  the 
presence  of  Calcium,  Barium, 
Strontium,  Manganese,  and 
Magnesium  ....  56 

Detection  of  a  Phosphate  in  the 

presence  of  Iron  .         .         56 

Separation  of  an  Arseniate  from 

a  Phosphate          ...         56 

Detection  of  Formates  in  the  pre- 
sence of  other  Organic  Acids  56 

Separation  of  Oxalates,  Tartrates, 

Citrates,  and  Malates  .         .         57 

Detection  of  Carbolic  Acid  in  the 

presence  of  Salicylic  Acid    .         57 

Test  for  Cinnamic  Acid  in  Ben- 
zoates   57 

Test  for  Chlorobenzoic  Acid   in 

Benzoic  Acid        •         •         •         57 

Test  for  Ilippuric  Acid  in  Benzoic 

Acid 57 

Test  for  Cresol  in  Phenol     .         .         57 

Special  Tests  for  Tartaric  Acid  in 

Citric  Acid  .         .         .         .         57 

Distinction  of  Salicylates  from 
Carbolates  and  Sulphocar- 
bolates  ....  57 

Test   for   Selenium  in  Sulphuric 

Acid     .  ...         57 


TABLE   OF  CONTEN1S. 


IX 


CHAPTER   IV. 
Qualitative  Analysis,  as  applied  to  the  Detection  of  Unknown  Salts. 


PAGE 

§  I.  General  Preliminary  Exami- 
nation .  .  .  .  $&-6o 

§  II.  Detection  of  the  Metal 
present  in  any  Simple 
Salt  (with  Tables  for 
same)  ....  61-64 

§  III.  Detection  of  the  Metals  in 
Complex  Mixtures  of  two 
or  more  Salts  (with  Tables 
for  same)  ....  65-74 


§    IV.    Detection       of 
Radicals    . 


the 


Acid 

.    75-80 


Div.  A.    Preliminary  Examina- 
tion       ...         75 
,,     B.  Preparation  of  Solution         77 

„      C.  Course    for    Inorganic 

Acids     ...         78 

„     D.  Course      for     Organic 

Acids     ...         80 
Solubility  Tables         .  82.  83 


TABLES. 

PAGE 

Full   table  for  the  Detection  of  the 
Metal  in  a  Solution  containing  one 

Base  only 62 

Table  for  the  Detection  of  the  Me'al 

in  a  Simple  Salt,  limited  to  Salts 

included  in  the  Pharmacopoeia        .         64 

Table  for  the  Detection  of  Metals  in 

mixtures    of   Pharmacopoeia    Salts 

Jacing  p.         74 
Table   for  the  Separation  of  Metals 

into  Groups 66 

Table  A.    Separation    of  Metals 

of  Group  1 67 

Table  B.    Separation   of   Metals 

of  Group  II.,  Div.  (a)      .         .         68 
Table  C.    Separation   of    Metals 

of  Group  II.,  Div.  (b)      .         .         69 
Table  D.   Separation    of  Metals 

of  Group  III.,  Div.  (a)    .         .         70 
Table  E.  Separation   of    Metals 
of  Group  III.,  Div.  (a),  in  pre- 
sence of  Phosphoric  Acid         .         71 
Table  F.    Separation    of  Metals 

of  Group  III.,  Div.  (b}   .         .         72 
Table  G.    Separation   of   Metals 

of  Group  IV 73 

Table  H.   Separation   of   Metals 

of  Group  V 74 


CHAPTER    V. 

Qualitative  Detection  of  Alkaloids  and  Certain  Organic  Bodies 

used  in  Medicine,  with  a  General  Sketch  of 

Toxicological  Procedure. 


Division  A.  Course  for  the  Detection  of  the  Alkaloids  and  Alkaloid  Salts  used  in 
Medicine,  together  with  a  general  Resume  of  the  Tests  for  all  the 
chief  Alkaloids  (as  under)  ........  84-87 


Aconitine. 

Apomorphine. 

Atropine. 

Beberine. 

Berberine. 

Brucine. 

Caffeine. 

Calabarine. 

Chelidonine. 

Cinchonine. 

Cinchonidine. 

Cocaine. 

Codeine. 


Colchicine. 

Colchice'ine. 

Coniine. 

Curarine. 

Delphinine. 

Delphinoidine. 

Emetine. 

Gelsemine. 

Homatropine. 

Hydrastinine. 

Hyoscine. 

Hyoscyamine. 

Jervine. 


Morphine. 

Narceine. 

Narcotine. 

Nepaline. 

Nicotine. 

Papaverine. 

Physostigmine. 

Pilocarpine. 

Piperine. 

Quinamine. 

Quinidine. 

Quinine. 

Sabadilline. 


Sabatrine. 

Solanine. 

Sparteine. 

Staphysagrine. 

Strychnine. 

Taxine. 

Thalictrine. 

Thebaine. 

Theobromine. 

Veratrine. 

Veratroidine. 


TABLE  OF  CONTENTS. 


Division  B.     Qualitative  Detection  of  certain  Organic  Bodies  commonly  employed 


Acetanilide.                  Chloral.                     Guaiacum  Resin. 
Acetic  Ether.               Chloroform.              lodoform. 
Adeps  Lanae.               Chrysarobin.            Jalap  Resin. 
Aloin.                            Creasote.                   Methyl  Alcohol. 
Amyl  Alcohol.             Elaterin.                   Naphthol. 
Amyl  Nitrite.               Ethyl  Alcohol.         Nitrobenzene. 
Antipyrin.                     Fel  Bovinum.           Paraldehyd. 
Benzin  (petroleum).    Gelatine.                   Phenacetin. 
Benzol  (benzene).       Glycerine.                 Picrotoxin. 
Division  C.     Qualitative  Analysis  of  Scale  Preparations    . 
„        D.     General  Sketch  of  the  Method  of  Testing  for  Poisons  in 

Podophyllin  Resin. 
Resin. 
Resorcin. 
Saccharine. 
Salol. 
Santonin. 
Scammony  Resin. 
Sugars. 
Sulphonal. 
.     91-92 
Mixtures         .     92-93 

PART    If.— QUANTITATIVE    ANALYSIS. 


CHAPTER  VI. 
Weighing,  Measuring,  and  Specific  Gravity, 


1.  Weighing  and  Measuring 

2.  Specific  Gravity 
(a)  Of  Liquids    . 
(6)  Of  Solids      . 


94-95 

96-103 

96-98 

98-99 


of 


(r)  Practical     Applications 

Specific  Gravity      .         .       99-100 
(</)  Of  Gases      ....     100-101 

(e)  Vapour  Density   .         .         .     101-103 
(/)  Note  on  Weights  and  Measures         103 


II. 


Ill 


CHAPTER   VII. 


Volumetric  Quantitative  Analysis. 


I.   Introductory  Remarks         .         .      104 

A.  Standard  Solutions     .         .     104 

B.  Indicators .         .         .         .105 

(1)  For  Acids  or  Alkalies     105 

(2)  For  Special  Purposes .      105 

C.  Apparatus  Employed.         .      106 

D.  Weighing  Operations          .      107 

E.  General  modus  operandi     .      107 

F.  Quantities  to  Weigh  .         .108 

G.  Direct  Titration          .         .     109 
H.  Residual  Titration      .         .109 

Alkalimetry        ....      109 

A.  Preparation  of  Acid  Solutions     109 
I.  Normal  Oxalic         .         .109 

II.  Tenth-normal  Oxalic        .     no 
in.  Normal  Sulphuric    .  110 

IV.  Half-normal  Sulphuric     .      110 
v.  Tenth-normal  Sulphuric  .      no 
vi.  Normal  Hydrochloric       .     no 
VII.  Half-normal  Hydrochloric     ill 

B.  Estimation  of  Alkaline  Hy- 

droxides and  Borax      .     in 

C.  Estimation  of  Alkaline  Car- 

bonates        .          .          .112 

D.  Estimation  of  Organic  Salts     112 

E.  ,,  ,,  Lead  Salts    .      113 
/"'.  Cases  for  Residual  Titration     113 

Acidimetry          .         .          .         .114 
Normal  Alkali         .         .         .114 

A.  Normal  Potash       .         .114 

B.  Half-normal  Potash        .     115 

C.  Normal  Soda          .         .      115 
D.  General  Acidimetry         .      115 

IV.  Standard   Solution    of    Argentic 

Nitrate    .  .116 


A.  Preparation 

B.  Estimation  of  Haloid  Salts 

C.  ,,  ,,  Hydrocyanic 
Acid      .... 

V.  Standard   Solution    of    Sodium 
Chloride 

A.  Preparation 

B.  Uses          .... 
VI.  Standard  Solution  of  Potassium 

Thiocyanate  . 

A.  Preparation 

B.  Estimation  of  Silver  in  Acid 

Solutions 

C.  Estimation  of  Haloid  Salts 

in  Acid  Solutions  . 
VII.   Standard  Solution  of  Iodine 

A.  Preparation 

B.  Estimation     of    Arsenious 

Acid      .... 

C.  Estimation   of    Sulphurous 

Acid  and  Sulphites 

D.  Estimation  of  Antimony     . 
VIII.   Standard    Solution   of    Sodium 

Thiosulphate  . 

A.  Preparation 

B.  Estimation  of  Free  Iodine  . 

C.  ,,          ,,      ,,   Chlorine 

&  Bromine 

D.  ,,          ,,  Available 

Chlorine    . 

E.  ,,  ,,  Ferric  Salts. 

F.  Assay  of  Reduced  Iron 
IX.   Standard  Solution  of  Bromine  . 

A.  Preparation 

B.  Estimation  of  Phenol 


116 
1 16 

117 

118 
118 
118 

119 
119 

119 

119 
1 20 

120 

120 

120 
120 

121 
121 
121 

121 

122 
122 
123 
123 
123 
124 


TABLE  OF  CONTENTS. 


xi 


X.  Analysis  by  Direct  Oxidation        .     124 

A.  General  Principles         .         .     124 

B.  Standard  Potassium  Perman- 

ganate    .         .         .         .126 

(1)  Preparation   and   Standard- 

isation   .         .         .          .126 

(a)  Solution  for  Immediate  Use     126 

(b)  Solution  for  Keeping         .      126 
(f]  Check  by  Ferrous  Salts     .     127 

(2)  Estimation  of  Ferrous  Salts     128 

(3)  Estimation  of  Oxalic  Acid 

and  Oxalates.         .         .128 

(4)  Estimation     of     Hydrogen 

Dioxides         .         .         .128 

(5)  Estimation  of  Nitrites          .      128 

C.  Standard   Potassium    Bichro- 

mate     .         .         .         .128 

(1)  Preparation         .         ,         .128 

(2)  Uses 128 

(a)  Estimation  of  Ferrous  Salts     128 
(b}  For  Alkalimetry        .         .129 

(c)  For     Equivalent     Libera- 

tion of  Halogens    .         .129 
XI.  Standard  Fehling's  Solution          .      129 


A.  Preparation 

B.  Estimation  by  Pavy's  Method 

C.  Estimation  of  Sugars  . 

D.  „          „  Starch  . 
XII.  Standard  Uranic  Nitrate  . 

Estimation  of  Phosphates 

XIII.  Standard  Barium  Chloride 

XIV.  Standard  Mayer's  Solution 
XV.  Analysis  of  Nitrometer 

A.  General  Remarks 

B.  Estimation  of  Sp.  ^Etheris 

Nit. 

C.  „          ,,  Amyl  Nitrite 
D.  ,,          ,,  Nitrates 

£•  ,,          ,,  Carbonates  . 

F.  „          ,,  Hydrogen 

Peroxide  . 

G.  „          „  Urea   . 
XVI.  Colorimetric  Analysis 

General  Remarks 

A.  Estimation  of  Ammonia     . 

B.  ,,          „  Nitrites 

C.  Estimation  of  Minute  Quan- 

tities of  Copper  or  Iron  . 


PAGE 
129 
130 


I32 
I32 
133 
133 

133 
134 
134 
134 

135 
135 

'3? 
I36 

136 

137 

137 


CHAPTER   VIII. 
Gravimetric  Quantitative  Analysis  of  Metals  and  Acids. 


Div.   I.   Preliminary  Remarks  . 

A.  Preparation  of  Filters  . 

B.  Estimation  of  Ash  of  Filters 

C.  Collection   and   Washing  of 

Precipitates 

D.  Drying  of  Precipitates . 
£.   Igniting   and    Weighing    of 

Precipitates 

F.  Estimation  of  Moisture 

G.  ,,  ,,  Ash  in  Organic 
Bodies     .... 

H.   Use  of  Analytical  Factors    . 


Div.    II.   Gravimetric    Estimation 
the  Metals 

1.  Estimation  of  Silver  : 

A.  As  Chloride 

B.  As  Metal    . 

2.  Estimation  of  Lead  : 

A.  As  Oxide    . 

B.  As  Chromate 

3.  Estimation  of  Mercury  : 

A.  As  Metal     . 

B.  As  Sulphide 

4.  Estimation  of  Cadmium  . 

5.  ,,  „   Copper: 

A.  As  Oxide    . 

B.  As  Metal     . 

6.  Estimation  of  Bismuth : 

A.  As  Sulphide 

B.  As  Oxide    . 

7.  Estimation  of  Gold . 

8.  ,,          ,,   Platinum    . 
9-           ,,          ,,  Tin  : 

A.  As  Oxide    . 

B.  As  Metal     . 

10.  Estimation  of  Antimony  . 


of 


138 
138 
139 

139 
140 

140 
141 

141 
142 


142 

142 
143 

143 


H3 
144 
144 

144 
144 


145 
145 
H5 

145 
146 
146 


11.  Estimation  of  Arsenic  : 

A,  As  Sulphide         .         .         .     146 

B.  As  Magnesium  Ammonium 

Arseniate          .         .         .     147 

12.  Estimation  of  Cobalt        .         .     147 

13.  Nickel        .         .     147 

14.  Manganese          .     147 

15.  Zinc  .         .         .     148 

1 6.  Iron  .         .         .148 

17.  Aluminium         .     148 

1 8.  Chromium.         .     148 

19.  Barium       .         .     149 

20.  Calcium      .         .149 

21.  Magnesium         .     149 

22.  Potassium  .         .150 

23.  Sodium       .         .     150 

24.  Potassium      and 
Sodium  in  presence  of  Metals 

of  the  Fourth  Group     .         .150 

25.  Indirect  Estimation  of  Potassium 

and  Sodium          .         .         .151 

26.  Estimation  of  Ammonium         .     151 
Div.   III.   Gravimetric    Estimation   of 

Acid  Radicals          .         .151 

1.  Chlorides          .         .         .         .     151 

2.  Iodides 151 

3.  Bromides          .         .         .         .151 

4.  Cyanides 151 

5.  Estimation  of  an  Iodide  in  the 

presence  of  a  Chloride  and 
Bromide     .         .         .         .152 

6.  Sulphides          .         .         .         .152 

7.  Sulphates          .         .         .         .     152 

8.  Nitrates 152 

A.  In  Alkaline  Nitrates    .         .152 

B.  As  Nitric  Oxide  .         .         .153 

C.  As  Ammonia        .         .         .153 


Xll 


TABLE  OF  CONTENTS. 


PAGE 

9.   Estimation  of  Phosphates         .     153 

A.  Estimation  of  the    Strength 

of  Free  Phosphoric  Acid  .     153 

B.  Alkaline  Phosphates    .         .     153 

C.  In  presence  of  Calcium  and 

Magnetism        .         .         -153 

D.  In    presence    of    Iron    and 

Aluminium       .         .         .154 

E.  Estimation      as      Phospho- 

molybdate         .         .         .154 
IO.   Estimation  of  the  * '  Total "  and 
"Soluble"  Phosphates  in 
a  Manure  or  Soil      .         .     154 


PAGE 

A.  Total  Phosphates          .  154 

B.  Soluble  Phosphates      .  155 
Estimation  of  Arseniates  .  155 

Carbonates  155 

Borates       .  156 

Oxalic  Acid  156 

Tartaric  Acid  156 

Silicic  Acid  157 

A.  In  Soluble  Silicates      .  157 

B.  In  Insoluble  Silicates  .  157 
Div.    IV.   Quantitative     Separations 

Full  Mineral  Analysis  of 

Water     .        .        ".         .  157 


II. 

12. 

13- 
14. 

II: 


CHAPTER    IX. 
Ultimate  Organic  Analysis. 


I.  Apparatus  Required     .         .         .160 
II.   Estimation   of  Carbon  and   Hy- 
drogen    .         .         .         .         .161 
ILL   Estimation  of  Nitrogen         .         .     164 
I.  Method       of       Varrentrapp 

Modified    .         .         .         .164 


II.  Original  Method  of  Varren- 
trapp        .         .         .  165 
ill.  Process  of  Dumas         .  165 
iv.   Kjeldahl's  Process        .  166 
IV.  Estimation  of  Chlorine.         .  166 
V.           ,,          ,,  Sulphur  and  Phos 

phorus 166 


CHAPTER   X. 
Special  Processes  for  the  Analysis  of  Water,  Air,  and  Food. 


Div.    I.     The    Sanitary    Analysis    of 

Water       .         .          .         .167 

1.  Collection  of  Sample  .         .        .     167 

2.  Color 167 

3-  Odor. 167 

4.  Suspended  Solids  .         .167 

5.  Total  Solids       .  .     167 

6.  Chlorine     .         .  .         .     168 

7.  Nitrogen  in  Nitrates  .         .168 

8.  Nitrites      .  .         .     169 

9.  Ammonia  and  Albuminoid  Am- 

monia     170 

10.  Oxygen  Consumed     .         .         .171 

11.  Hardness 172 

12.  Judging  the  Results   .         .         .173 


Div.  IF.    The  Sanitary  Analysis  of  Air 

1.  Testing  for  Gaseous  Impurities  . 

2.  Estimation  of  Carbon  Dioxide    . 
3-  ,,          ,,  Organic  Matter     . 

Div.  III.   Food  Analysis     . 


174 
174 
174 
174 


1.  Milk 175 

Table  Degrees  of  Thermometer  .     176 

2.  Butter 178 

3.  Alcohol  (Estimation  of)     .         .178 
Table  Percentages  of  Alcohol     .     179 

4.  Bread  and  Flour         .         .         .180 

5.  Mustard 181 

6.  Pepper 181 

7.  8.  Coffee  and  Colored  Sweets     .     182 
9.  Vinegar 182 


CHAPTER   XI. 


Special  Processes  for  the  Analysis  of  Drugs,  Urine,  and  Urinary  Calculi. 


Div.  I.  Analysis  of  Drugs  .  .  .  184 
I.  General  Scheme  .  .  .184 
n.  Alkaloidal  Assay  by  Immiscible 

Solvents  .         .         .         .186 
in.  Assays  of  Drugs   where    Alka- 
loidal Residue  is  Weighed  187 

(1)  Alkaloidal  Scales         .         .  187 

(2)  Colchicum  and  Preparations  187 

(3)  Coniuni  and  Preparations    .  189 

(4)  Cinchona  and  Preparations  190 

(5)  Guarana  and  Preparations  .  192 

(6)  Hydrastis  and  Preparations  192 

(7)  Opium  and  Preparations      .  193 
IV.  Titration    of    Alkaloidal    Resi- 
dues        ....  195 


v.  Assays  of  Drugs  where  Residue 

is  Titrated        .         .         .  196 

(1)  Aconite  and  Preparations    .  196 

(2)  Drugs  containing  Mydriatic 

Alkaloids          .          .          .  196 

(3)  Coca  and  Preparations         .  199 

(4)  Ipecac,  and  Preparations     .  201 

(5)  Nux    Voniica  and  Prepara- 

tions         ....  2OI 

(6)  Pilocarpus  and  Preparations  204 

(7)  Physostigma   and    Prepara- 

tions        .         .          .          .20; 

'I.  Assay  of  Digestive  .Ferments      .  206 

(a)  Pepsin     .         .         .         .206 

(b)  Pancreatin       .         .         .  206 


TABLE  OF  CONTENTS. 


Div.  I.  Analysis  of  Drug?  (continued): 

vil.  Examination     of     Resins     and 

Gum-resins         .  .     206 

(a)  Acid  Number  Process  .     206 

(£)  Asafetida      .         .  .     206 

(c)  Guaiacum     .         .  .     206 

(d)  Jalap    ...  .206 

(e)  Myrrh.          .  .207 
(/)  Podophyllum         .  .     207 
(g)  Rosin  ...  .     207 
(ft)  Scammony  .         .                   .     207 

viii.  Examination  of  Balsams  .     207 

(a)  Benzoin        .         .  .     207 

(b)  Peru     ...  .     207 

(c)  Tolu     ...  .     207 

(d)  Storax.         .         .  .     207 
ix.  Examination  of  Tinctures,  etc., 

for  Methylated  Spirit          .     207 
x.  Analysis  of  Fixed  Oils  and  Fats     208 

(1)  Specific  Gravity    .         .         .     208 

(2)  Iodine  Absorption         .          .     209 

(3)  Saponification  Equivalent      .     209 

(4)  Specific  Heating  Power         .     210 

(5)  Qualitative  Tests  for  U.S.P. 

Oils 210 

(6)  Unsaponifiable  Matters  in  Oils     212 

(7)  Free  Acids  in  Oils        .         .212 
xi.  Analysis  of  Waxes    .         .         .212 

(1)  Beeswax       ....     212 

(2)  Non-official  Waxes        .         .214 


xii.  Analysis  of  Soap 

(1)  Estimation  of  Fatty  Acids 

(2)  General  Analysis  . 
xili.  Analysis  of  Essential  Oils 

1.  Physical  Constants 

2.  Solubility 

3.  Chemical  Analysis          . 
Qualitative  Tests    . 
Quantitative  Processes   . 

(a)  Esters 

(b)  Phenols 

(c)  Aldehyds     . 

(d)  Ketones 

(e)  Alcoholic  Bodies 
(/)  Isothiocyanates    . 

Div.  II.  Analysis  of  Urine. 

1.  Specific  Gravity 

2.  Reaction  .... 

3.  Deposit     .... 

4.  Albumin  (and  estimation)  . 

5.  Sugar  (and  estimation) 

6.  Bile 

7.  Urea  (and  estimation) 

8.  Uric  Acid  (and  estimation) 

9.  Phosphates 

10.  Sulphates. 

11.  Chlorides  .... 

12.  Blood        .... 
Div.  III.  Analysis  of  Urinary  Calculi 

(a)  Organic 

(b)  Inorganic 


PAGE 
215 
215 
2I5 

215 
215 

217 
217 

317 
217 

217 

218 

218 

219 
219 

222 
222 
222 
222 
222 
222 
224 
225 
225 
225 
226 
226 
226 
226 
227 
227 
227 


CHAPTER   XII. 
Analysis  of  Gases,  Polarisation  and  Spectrum  Analysis,  etc. 

I.   The  Taking  of  Melting,  Solidifying,  and  Boiling  Points       ....  228 

II.  Analysis  by  the  Polariscope        .  229 

III.  Spectrum  Analysis 231 

IV.  Analysis  of  Gases  by  Hempel's  Method 232 


APPENDIX. 


List  of  Atomic  Weights 


236 


PART   /. 

QUALITATIVE   ANALYSIS. 


CHAPTER    I. 
THE  PROCESSES  EMPLOYED  BY  PRACTICAL  CHEMISTS. 

IT  is  advisable  that  the  student  should  understand  the  raison  d'etre  of  the 
chief  processes  he  will  be  called  upon  to  employ,  before  commencing  in  detail 
the  study  of  Analysis. 

I.  SOLUTION. 

This  process  consists  in  leaving  a  solid  body  in  contact  with  a  fluid  until 
it  dissolves,  heat  being  occasionally  used.  Bodies  which  refuse  to  dissolve 
in  any  particular  fluid  are  said  to  be  insoluble  in  it ;  the  liquid  used  is  called 
the  solvent,  and  sometimes  the  menstruum ;  a  liquid  having  taken  up  all  the 
solid  matter  possible  is  said  to  be  saturated.  A  knowledge  of  the  solubility 
of  various  substances  in  the  chief  menstrua,  such  as  water,  acids,  alkalies, 
alcohol,  ether,  chloroform,  and  glycerine,  is  of  the  utmost  importance,  because 
we  are  thus  enabled  to  separate  one  body  from  another ;  and,  by  attention  to 
minute  details,  it  is  possible  to  part  bodies  which  are  soluble  in  the  same 
menstruum,  but  in  different  degrees,  the  process  being  called  fractional 
solution.  In  order  to  ascertain  if  any  substance  be  soluble  in  any  particular 
liquid,  it  is  simply  requisite  to  place  it  in  the  fluid,  applying  heat  if  necessary. 
A  portion  of  the  liquid  is  then  poured  off,  and  evaporated  to  dryness,  when, 
if  any  of  the  solid  be  held  in  solution,  it  will  remain  as  a  visible  residue. 
As  a  general  rule,  the  higher  the  temperature  to  which  a  liquid  is  raised,  the 
greater  becomes  its  capacity  for  saturation.  There  are,  however,  exceptions 
to  this  rule — notably  that  of  calcium  oxide,  which  is  less  soluble  in  boiling 
water  than  in  cold.  Many  bodies,  during  solution,  absorb  so  much  heat  that 
any  substance  placed  in  the  liquid  has  its  temperature  remarkably  reduced. 
Sodium  sulphate,  dissolved  in  hydrochloric  acid,  forms  in  this  manner  a  very 
efficient  refrigerant  when  snow  or  ice  is  not  obtainable. 

II.  LIXIVIATION  AND  EXTRACTION. 

These  processes  include  the  digestion  of  a  mixture  of  solids  in  a  fluid,  so 
as  to  dissolve  the  soluble  portion.  The  solids,  in  the  form  of  powder,  are 

i  i 


CHEMICAL  PROCESSES. 


introduced  into  a  vessel,  and  the  water  or  other  liquid  having  been  added, 
the  whole  is  well  stirred.  Remaining  at  rest  until  all  the  insoluble  matter  has 
subsided,  the  clear  fluid,  charged  with  all  that  was  soluble  in  the  mixture,  is 
decanted,  or  drawn  off  by  means  of  a  syphon. 

When  a  substance  is  to  be  extracted  by  means  of  a  readily  volatile  solvent, 
such  as  ether  or  chloroform,  the  arrangement  used  is  that  known 
as  Soxhlet's  apparatus.     This  is  illustrated  in  fig  i.     A  flask  (A) 
is  charged  with  the  solvent.    The  substance  (E)  is  put  into  a 
cartridge  of  filtering  paper,  and  introduced  into  the  Soxhlet  tube 
(D)  ;  the  latter  is  in  turn  connected  with  the  upright  condenser 
(c),  through  the  jacket  of  which  a  stream  of  cold  water  is  made 
to  pass.     Heat  is  now  applied  to  the  flask  by  a  water  bath,  and 
the  vapour  of  the  ether,  rising  through  B,  condenses  and  drops 
on  to  the  powder  in  the  cartridge.     When  the  instrument  has 
become  filled  by  the  condensed  solvent  to  the  level  of  the 
top  of  F,  it  runs  back  into  the  flask,  charged  with  the  soluble 
matter  that  has  been  extracted.     This  process  then  repeats 
itself  until  the  whole  soluble  portion  has  been  extracted  and 
transferred  to  the  flask,  which  latter  may  then  be  attached  to 
an  ordinary  condenser,  and  the  solvent  distilled  off,  leaving 
the   soluble   matters   of  the   original   powder   in   the  flask. 
Resinous   and   sticky  substances  should   be  mixed  with   a 
little  purified   sand   to  prevent  their   clogging   up   the  ap- 
paratus. 

Another  method  of  extraction  is  that  known  as  percolation, 
a  process  much  used  in  pharmacy.  The  ap- 
paratus employed  is  illustrated  in  fig.  2.  The 
upper  portion  (A)  is  the  percolator,  in  which 
the  powder  to  be  extracted  is  tightly  packed 
and  the  solvent  having  been  poured  upon  it, 
the  whole  is  allowed  to  macerate  for  some 
time.  The  stopcock  (c)  being  then  opened,  Fi£- x- 

c  the  fluid  gradually  filters  into  the  receiver  (B),  and  more  solvent  is 
then  poured  on  until  the  soluble  portion  of  the  contents  of  the 
percolator  has  been  entirely  transferred  to  the  receiver.  The  con- 
necting tube  is  to  prevent  loss  of  volatile  solvents. 

III.   PRECIPITATION. 

This  process  consists  in  mixing  the  solutions  of  two  substances 
Fig.  a.      so  as  to  form  a  third  substance,  which,  being  insoluble  in  the  fluids 
employed,  sinks  to  the  bottom,  and  is  called  the  precipitate.     The 
clear  liquid  which  remains  after  the  precipitate  has  settled  down  is  called  the 
supernatant  liquid. 

When  precipitates  are  totally  insoluble  in  water  (such  as  barium  sulphate 
or  argentic  chloride),  the  operation  is  best  conducted  at  a  boiling  heat,  the 
high  temperature  causing  the  precipitate  to  aggregate,  so  that  it  subsides 
rapidly,  and  is  less  liable  to  pass  through  the  pores  of  the  filter.  On  the 
other  hand,  there  are  some  precipitates  which  must  never  be  heated,  but  be 
allowed  to  form  slowly  by  standing  in  the  cold  for  several  hours.  To  this 
class  belong  ammonium-magnesium  phosphate,  and  acid  potassium  tartrate. 
When  it  is  desirable  to  cause  precipitates  to  form  quickly,  resort  may  be 
had  to  stirring  with  a  glass  rod,  so  that  it  scrapes  against  the  sides  of  the 
vessel. 

In  qualitative   analysis  precipitation   is   usually  conducted   in   test-tubes 


DECANTA  TION—FILTRA IION—DISTILLA  TION.  3 

shown  in  fig.  3.     These  are  kept  in  a  stand  (fig.  4)  having  holes  for  the 
reception  of  tubes  actually  in  use,  and  also  a  row  of  pegs  upon  which  freshly- 


Fig.  3- 


Fig.  4 


Fig.  5- 


Fig.* 


washed  tubes  may  be  inverted  to  drain.  Fig.  5  illustrates  the  appliance 
used  to  hold  tubes  when  their  contents  are  to  be  boiled,  and  fig.  6  shows  the 
brush  used  for  cleansing  them. 

In  quantitative  analysis  precipitation  is  generally  performed  in  beakers. 
These  are  very  thin  tumblers  made  of  glass,  free  from  lead,  and  annealed  so 
as  to  permit  their  use  with  boiling  liquids  without  risk  of  fracture. 

Precipitates  are  separated  from  the  supernatant  liquor  by  one  of  two- 
methods.  First : — 

IV.   DECANTATION, 

which  consists  in  allowing  the  precipitate  to  settle  to 
the  bottom,  and  pouring  off  the  clear  liquor.  This  is 
best  done  by  the  use  of  a  glass  rod  held  as  shown  in  the 
illustration,  fig.  7.  Second  : — 


PIC7. 


V.   FILTRATION, 

which  consists  in  transferring  the  whole  to  a  piece  of  folded  filtering-paper 
or  cloth  placed  in  a  funnel,  so  that  the  liquid  passes  through,  while  the 
precipitate  remains.  The  liquor  which  has  thus  passed  through  the  filter  is 
called  the  filtrate. 

Specially  prepared  circular  papers  for  filtration  are  sold,  and  they  have  only 
to  be  folded  to  fit  the  funnel  for  which  they  are  destined.     The  illustrations- 


Fig.  8. 


Fig.  9. 


show,  hg.  8  ^A),  the  circle  of  paper,  and  (B)  the  same  as  folded  for  use,  while 
fig.  9  represents  the  whole  arrangement  ready  for  use. 


VI.   DISTILLATION. 

When  a  liquid  is  converted  into  vapour  by  the  aid  of  heat,  and  the  vapour 
is  passed  through  a  cooling  apparatus,  called  a  condenser,  its  latent  heat  is 


CHEMICAL  PROCESSES. 


abstracted,  and  it  is  deposited  as  a  liquid  again.  The  process  is  called 
distillation.  It  is  used  to  separate  a  volatile  liquid  from  non-volatile  substances. 
The  liquid  which  passes  over  and  is  condensed  in  the  receiver  is  called  the 

distillate ;  while  the  non-volatile  matter 
which  remains  in  the  retort  is  called  the 
residue.  Figure  10  shows  the  arrangement 
most  commonly  used  in  laboratories  for 
small  distillations.  A  is  the  retort  in  which 
the  fluid  is  boiled,  and  B  is  called  a  Liebig's 
condenser  (through  the  jacket  of  which  a 
stream  of  water  is  caused  to  pass),  and 
beneath  the  end  of  this  is  placed  a  vessel 
(c)  for  the  reception  of  the  distillate.  By 
careful  attention  to  their  boiling  points, 
various  volatile  fluids  may  thus  be  separated  from  each  other.  Suppose,  for 
example,  that  we  have  a  mixture  of  three  substances  boiling  respectively  at 
80°,  100°,  and  120°,  and  their  separation  is  desired,  we  should  introduce  the 
mixture  into  a  retort  fitted  with  a  thermometer,  the  bulb  of  which  was  placed 
ju'ot  above  the  level  of  the  fluid.  The  whole  being  then  attached  to  the 
condenser,  the  heat  would  be  gradually  raised  until  the  thermometer  marked 
£0°,  and  that  temperature  would  be  steadily  maintained  as  long  as  anything 
continued  to  collect  in  the  receiver.  When  this  ceased,  the  receiver  would 
be  changed,  the  temperature  raised  to  100°,  and  the  distillation  continued 
until  the  second  liquid  had  ceased  to  pass  over.  The  receiver  being  ones 
more  changed,  the  heat  would  be  again  raised,  and  maintained  until  the  last 
liquid  had  been  obtained  as  a  distillate.  This  process  is  called  fractional 
distillation. 

VII.   SUBLIMATION. 

When  a  solid  is  converted  into  vapour  by  heat,  and  again  deposited  'in 
•changed  in  the  solid  form  in  a  cooled  vessel,  it  is  said  to  have  been  subjected 
to  sublimation.  Sublimation  is  used  to  separate  volatile  from  non-volatile 
solids,  and  is  thus  conducted  : — The  substance  to  be  sublimed  is  thinly 
spread  over  the  bottom  of  a  shallow  iron  pan,  covered  with  a  sheet  of  bibulous 
paper  perforated  with  numerous  pin-holes,  or  with  a  piece  of  muslin.  By 
means  of  a  sand  bath,  the  heat  is  slowly  raised  to  the  desired  degree,  when 
the  vapour,  passing  through  the  strainer,  condenses  in  a  cap  of  wood  or 
porcelain,  lined  with  stout  cartridge  paper,  previously  placed  over  the  heating- 
pan  and  kept  cool.  Fractional  sublimation  is  often  useful,  and  may  be 
employed  in  a  similar  manner  to  fractional  distillation. 

VIII.   FUSION 

is  the  liquefaction  of  a  solid  by  the  aid  of  heat.  It  is  usually  carried  out  in 
a  vessel  called  a  crucible.  For  the  purposes  of  analysis,  fusion  is  generally 


conducted  in  porcelain,  platinum,  or  silver  crucibles,  according  to  the  nature 
of  the  substance  under  examination  ;    but  alkalies  should  be  fused  only  in 


EVAPORATION— CRYSTALLISATION  AND  DIALYSIS.        5 

crucibles  made  of  the  latter  metal.  A  peculiar  kind  of  fusion,  called  cupella- 
tion,  is  resorted  to  in  the  assay  of  gold  and  silver  bullion.  The  alloy  to  be 
assayed  is  wrapped  in  a  piece  of  lead  foil,  and  the  whole  is  then  heated  in 
a  little  cup  made  of  bone  ash,  called  a  cupel,  when  the  lead,  copper,  etc., 
oxidise,  fuse,  and  sink  into  the  substance  of  the  porous  cupel,  leaving  the  non- 
oxidisable  metals  as  a  metallic  button,  which  may  then  be  weighed.  The 
illustration  (fig.  u)  shows  a  set  of  crucibles  for  fusion — A  being  of  fire-clay  ; 
B,  a  platinum  crucible ;  c,  one  of  porcelain  ;  and  D,  what  is  called  Roses 
crucible,  for  heating  substances  in  a  current  of  hydrogen  when  it  is  desired  to 
prevent  access  of  air,  or  to  produce  rapid  reduction  to  the  metallic  state. 

IX.   EVAPORATION 

consists  in  heating  a  liquid  until  the  whole,  or  as  much  of  it  as  may  be 
required,  passes  off  in  vapour.  A  solution  thus  treated  until  it  has  wholly 
passed  into  vapour  is  said  to  be  evaporated  to  dryne-ss,  and  any  solid 
substance  remaining  is  called  the  residue. 

Solutions  containing  organic  or  volatile  bodies  ought  always  to  be  evaporated 
on  a  water  bath  ;  that  is,  in  a  vessel  exposed  only  to  the  heat  of  boiling 
water,  in  which  the  temperature  must  always  be  below  100°  C.  Evaporation 
may  be  conducted  slowly,  without  raising  the  fluid  to  its  boiling  point,  when 
it  is  called  simply  vaporisation;  but  when  sufficient  heat  is  applied,  the 
evaporation  takes  place  rapidly,  and  is  accompanied  by  the  disengagement  of 
bubbles  of  vapour,  and  the  fluid  is  then  said  to  be  in  a  state  of  ebullition. 
All  liquids  possess  the  continual  desire,  as  it  were,  to  pass  into  vapour,  and 
the  vapour  formed  endeavours  to  expand  indefinitely ;  the  pressure  which  is 
thus  exerted  by  the  vapour  on  the  sides  of  the  vessel  containing  it,  is  called 
its  tension,  and  is  measured  by  the  height  of  the  column  of  mercury  it  is  able 
to  sustain.  The  more  the  liquid  is  heated,  the  greater  becomes  its  tendency 
to  vaporise,  and  consequently  the  more  powerful  is  the  tension  of  its  vapour ;; 
and  when  the  latter  is  sufficiently  marked  to  overcome  the  pressure  exerted: 
by  the  atmosphere  and  the  cohesion  of  the  liquid  itself,  ebullition  takes  place. 
The  boiling  point  of  a  fluid  is  therefore  the  temperature  at  which  the  tension  of 
its  vapour  just  exceeds  the  pressure  of  the  superincumbent  atmosphere.  If  the 
pressure  of  the  atmosphere  be  increased  artificially,  the  boiling  point  of  the 
liquid  will  rise  in  proportion.  As  steam  under  pressure  can  thus  be  obtained 
at  high  temperatures,  it  is  made  use  of  for  the  rapid  evaporation  of  liquids  on  a 
large  scale,  by  causing  it  to  pass  into  a  jacket  surrounding  the  evaporating 
pan.  The  apparatus  thus  made  use  of  is  called  a  steam  bath^  the  heat  of 
which  is  officially  understood  to  be  about  110°  C. 

If  water  be  boiled  in  a  chemically  clean  glass  vessel,  and  more  particularly- 
if  a  precipitate  be  suspended  in  the  water,  the  boiling  does  not  take  place 
regularly,  but  the  liquid  becomes  heated  above  its  boiling  point,  and  suddenly 
rushes  into  vapour  in  gusts.  This  is  called  by  practical  chemists  "  bumping," 
and  may  be  prevented  by  putting  in  a  few  fragments  of  platinum  foil,  the  air 
condensed  on  the  surface  of  which,  acting  as  a  nucleus,  aids  in  the  regular 
disengagement  of  the  vapour. 

X.   CRYSTALLISATION  AND  DIALYSIS. 

Many  substances  when  dissolved  in  a  boiling  liquid  separate  out,  as  soon 
as  the  fluid  cools,  in  masses  having  a  well-defined  and  symmetrical  shape, 
bounded  by  plain  surfaces  and  regular  angles.  These  bodies  are  named 
crystalline;  the  deposited  masses,  crystals;  and  the  remaining  solution,  the 
mother  liquor.  Substances  which  are  not  susceptible  of  crystallisation  are 


CHEMICAL   PROCESSES. 


called  amorphous  (i.e.,  formless)  bodies ;  while  solids,  such  as  glue  and  gums, 
which  are  soluble  in  water  and  yet  not  crystallisable,  are  named  colloids. 
Crystallisation  may  also  occur  during  solidification  after  fusion,  and  by  the 
spontaneous  evaporation  of  liquids  holding  crystalline  substances  in  solution. 
All  crystalline  bodies  invariably  assume  the  same  forms,  and  may  thus  be 
unmistakably  recognised  from  each  other.  The  process  is  also  useful  for 
purification,  as  at  the  moment  of  crystallisation  impurities  are  rejected,  and 
may  be  poured  off  with  the  mother  liquor.  Many  circumstances  affect  the 
size  of  the  crystals  produced  in  any  solution ;  as  a  rule,  the  more  rapidly 
crystallisation  takes  place,  the  smaller  are  the  crystals.  An  example  of  the 
extreme  variation  in  the  size  of  the  crystals  produced  from  the  same  solution 
«nay  be  seen  in  ferror*  sulphate.  When  allowed  to  deposit  slowly,  we  have 
the  ordinary  well-marked  commercial  crystals  ;  but  the  same  salt  dissolved  in 
boiling  water,  and  the  solution  suddenly  poured,  with  constant  stirring,  into 
•spirit,  gives  granulated  ferrous  sulphate  in  crystals  so  minute  that  a  lens  is 
^required  to  distinguish  them.  For  the  formation  of  large  and  well-defined 
crystals  perfect  rest  is  required,  and  it  is  often  desirable  to  introduce  pieces  of 
wood  or  string  so  as  to  form  nuclei  on  which  the  crystals  collect.  Good  examples 
are  seen  in  commercial  crystallised  sugar-of-milk  and  sugar-candy.  Some  bodies 
are  capable  of  crystallising  in  two  or  more  forms,  and  are  called  di-  tri-  or 
poly-morphous.  Instances  of  this  property  may  be  seen  in  mercuric  iodide 
.  and  in  sulphur. 

When  crystalline  substances  exist  in  a  solution  together  with  uncrystallisable 
colloid  bodies,  their  mutual  separation  is  effected  by  dialysis.     This  process 
-consists  in  introducing  the  mixture  into  a  glass  vessel  having  a  bottom  ma'de 
-of  vegetable   parchment.      This,  called  the  dialyser,  is  floated  in   a   large 
quantity  of  distilled  water  in  a  basin.     At  the  expiration  of 
several  hours  the  crystalline  bodies  will  have  passed  through 
the  parchment,  and  will  have  become  dissolved  in  the  water 
in  the  basin,  while  the  colloids  remain  in  the  dialyser.     This 
process  is  sometimes  employed  for  the  separation  of  crystal- 
line poison,  like  strychnine,  from  the  contents  of  a  stomach. 
The  rapidity  of  the  dialysis  is  greatly  increased  by  causing 
a  stream  of  water  to  pass  through  the  outer  basin,  but  of 
course  this  is  only  applicable  where  it  is  desired  to  retain 
the  colloid  body  and  not  the  crystalloid,  as  in  the  manufacture 
of  the  preparation  known  as  dialysed  iron.     The  apparatus  used  is  shown  in 
the  illustration  (fig.   12),  in  which  A  is  the  dialyser  containing  the  mixture, 
while  B  contains  the  water  into  which  the  crystalline  matter  passes. 

XI.   ELECTROLYSIS 

is  the  decomposition  of  bodies  by  means  of  electricity.  The  current  of 
electricity  is  obtained  from  a  voltaic  or  galvanic  cell  or  element,  and  a  com- 
bination of  several  cells  is  termed  a  battery.  Bunsen's  battery,  which  is  very 
extensively  used,  consists  of  an  outer  cell  or  jar  of  glazed  earthenware  in 
which  is  placed  a  cylinder  of  zinc,  an  inner  unglazed  porous  jar  and  a  rod  of 
carbon,  both  furnished  with  binding-screws  for  attaching  wires  to  them.  The 
acids  used  are  dilute  sulphuric  around  the  zinc,  and  strong  nitric  in  contact 
with  the  carbon  in  the  inner  cell.  The  upper  end  of  the  carbon  rod  is  called 
the  positive  pole,  while  that  of  the  zinc  plate  is  the  negative  pole  of  the  cell. 
The  ends  of  the  wires  leading  from  these  are  called  electrodes  ;  the  wire  from 
the  carbon  being  the  anode,  and  that  from  the  zinc  the  kathode.  On  con- 
necting these  electrodes,  a  current  of  electricity  passes  along  the  wire  which 
is  assumed  to  flow  from  the  positive  to  the  negative  pole.  Any  compound 


PYROLOGY. 


liquid  which  conducts  electricity  is  called  an  electrolyte,  and  when  the 
electrodes  of  a  battery  are  immersed  therein,  it  is  decomposed  into  simpler 
bodies  called  "ions";  those  thus  formed  at  the  anode  being  anions,  and 
those  liberated  at  the  kathode  being  kathions.  For  instance,  with  a  solution 
of  HC1,  Cl  is  given  off  at  the  anode,  and  H  at  the  kathode,  and  the  ions  are 
the  bodies  thus  directly  liberated.  Dealing  with  H2SO4,  on  the  other  hand, 
the  first  ions  are  H^  at  the  kathode,  and  SO4  at  the  anode ;  the  latter, 
however,  at  once  splitting  up  into  O  (given  off)  and  SO3,  which  re-forms 
H2SO4  with  the  water  present. 

Further  reference  to  applications  of  electrolysis  will  be  found  in  Chapter  X., 
when  the  student  arrives  at  quantitative  analysis.  It  is  also  applied  in  a 
modified  form  in  qualitative  analysis  to  the  separation  of  tin  and  antimony. 

XII.  PYROLOGY. 

Under  this  name  are  included  all  processes  of  analysis  depending  for  their 
action  on  the  use  of  fire,  or  in  other  words,  what  are  often  called  "reactions 
in  the  dry  way."  The  chief  instruments  used  are  the  Bunsen  burner  and 
the  blowpipe.  The  blowpipe  is  a  tube  with  a  narrow  nozzle,  by  which  a  con- 
tinuous current  of  air  can  be  passed  into  an  ordinary  flame.  The  ordinary 
gas  flame  consists  of  three  parts  :  (a)  A  non-luminous  nucleus  in  the  centre  ; 
(b)  A  luminous  cone  surrounding  this  nucleus  ;  and  (c)  An  outer  and  only 
slightly  luminous  cone  surrounding  the  whole  flame.  The  centre  portion  (a) 
contains  unaltered  gas,  which  cannot  burn  for  want  of  oxygen,  that  necessary 
element  being  cut  off  by  the  outer  zones.  In  the  middle  portion  (b)  the  gas 
comes  in  contact  with  a  certain  amount  of  oxygen,  but  not  enough  to  produce 
complete  combustion ;  and  therefore  it  is  chiefly  the  hydrogen  which  burns 
here,  the  carbon  separating  and,  by  becoming  intensely  ignited,  giving  the 
light.  '  In  the  outer  zone  (c)  full  combustion  takes  place,  and  the  extreme 
of  heat  is  arrived  at,  because  chemical  action  is  most  intense.  The  outer 
flame  therefore  acts  readily  on  oxidisable  bodies,  because  of  the  high  tem- 
perature and  the  unlimited  supply  of  air,  while  the  luminous  zone  tends  to 
take  away  oxygen  by  reason  of  the  excess  of  unburned  carbon  or  hydrocarbons 
therein  existing.  For  these  reasons  the  former  is  called  the  oxidising1  flame, 
and  the  latter  the  reducing  flame.  The  effect  of  blowing  air  across  a  flame  is, 
first,  to  alter  the  shape  of  the  flame,  which  is  at  once  lengthened  and  nar- 
rowed ;  and,  in  the  second  place,  to  extend  the  sphere  of 
combustion  from  the  outer  to  the  inner  part  (see  fig.  1 2  a). 
As  the  latter  circumstance  causes  an  increase  of  the  heat  of 
Fig.  iaa.  the  flame,  and  the  former  a  concentration  of  that  heat  within 

narrower  limits,  it  is  easy  to  understand  the  great  heat  of  the 
blow-pipe  flame.  The  way  of  holding  the  blowpipe  and  the  strength  of  the 
blast  always  depends  upon  whether  the  operator  wants  a  reducing  or  an 
oxidising  flame.  The  reducing  flame  is  produced  by  keeping  the  jet  of  the 
blowpipe  just  on  the  border  of  a  tolerably  strong  gas  flame,  and  driving  a 
moderate  blast  across  it.  The  resulting  mixture  of  the  air  with  the  gas  is  only 
imperfect,  and  there  remains  between  the  two  parts  of  the  flame  a  luminous 
and  reducing  zone,  of  which  the  hottest  point  lies  somewhat  beyond  the  apex 
of  the  inner  cone.  To  produce  the  oxidising  flame,  the  gas  is  lowered,  the 
jet  of  the  blowpipe  pushed  a  little  farther  into  the  flame,  and  the  strength  of 
the  current  somewhat  increased.  This  serves  to  effect  an  intimate  mixture 
of  the  air  and  gas  and  an  inner  pointed,  bluish  cone,  slightly  luminous 
towards  the  apex,  is  formed,  and  surrounded  by  a  thin,  pointed,  light-bluish, 
barely  visible  mantle.  The  hottest  part  of  the  flame  is  at  the  apex  of  the 
inner  cone.  Difficultly  fusible  bodies  are  exposed  to  this  part  to  effect  their 


CHEMICAL  PROCESSES 


fusion;  but  bodies  to  be  oxidised  are  held  a  little  beyond  the  apex,  that 
there  may  be  no  want  of  air  for  their  combustion. 

The  current  is  produced  by  the  cheek  muscles  alone,  and  not  with  the 
lungs.  The  way  of  doing  this  may  be  easily  acquired  by  practising  for  some 
time  to  breathe  quietly  with  puffed-up  cheeks  and  with  the  blowpipe  between 
the  lips  :  with  practice  and  patience  the  student  will  soon  be  able  to  produce 
an  even  and  uninterrupted  current. 

The  supports  on  which  substances  are  exposed  to  the  blowpipe  flame  are 
generally  either  wood  charcoal,  or  platinum  wire  or  foil. 

Charcoal  supports  are  used  principally  in  the  reduction  of  metallic  oxides, 
etc.,  or  in  trying  the  fusibility  of  bodies.  The  substances  to  be  operated 
upon  are  put  into  small  conical  cavities  scooped  out  with  a 
penknife.  Metals  that  are  volatile  at  the  heat  of  the  reducing 
flame  evaporate  wholly  or  in  part  upon  the  reduction  of  their 
oxides ;  in  passing  through  the  outer  flame  the  metallic  fumes 
are  re-oxidised,  and  the  oxide  formed  is  deposited  around  the 
portion  of  matter  upon  the  support.  Such  deposits  are  called 
Fig  123  N  incrustations.  Many  of  these  exhibit  characteristic  colours 
leading  to  the  detection  of  the  metals.  Thoroughly  burnt  and 
smooth  pieces  of  charcoal  only  should  be  selected  for  supports  in  blowpipe 
experiments,  as  imperfectly  burnt  and  knotty  pieces  are  apt  to  spirt  and  throw 
off  the  matter  placed  on  them.  The  method  of  employing  a  charcoal  support 
is  shown  in  fig.  12  b, 

The  great  use  of  charcoal  lies  (i)  in  its  low  degree  of  conductivity  :  (2)  its 
porosity,  which  causes  it  to  absorb  many  fusible  bodies  and  leave  infusible 
ones  upon  its  surface ;  and  (3)  its  power  of  aiding  the  effects  of  the  reducing 
flame. 

Platinum  wire  and  foil  are  used  for  supports  in  the  oxidising  flame,  and 
the  former  is  specially  employed  for  trying  the  action  of  fluxes  and  the  colour 
communicable  to  the  blowpipe  or  Bunsen  flame.  The  platinum  wire,  when 
employed  for  making  beads  of  borax  or  other  fluxes,  should  be  about  3  to  4 
inches  long,  with  the  end  twisted  into  a  small  loop.  The  loop  is  then  heated, 
and  dipped  while  hot  in  the  powdered  borax,  when  it  takes  up  a  quantity, 
which  is  then  heated  till  it  fuses  to  a  clear  bead  formed  within  the  loop. 
When  cold,  this  bead  is  moistened,  dipped  in  the  powder  to  be  tested,  and 
again  exposed  to  the  flame,  and  the  effect  noted.  For  trying  the  colour 
imparted  to  the  flame  by  certain  metals,  the  wire  is  first  cleaned  by  boiling 
in  dilute  nitric  acid  and  then  holding  it  in  the  flame  until  no  colour  is 
obtained.  The  loop  is  then  dipped  in  the  solution  to  be  tested,  and  held 
near  the  flame  till  the  adhering  drop  has  evaporated  to  dryness,  and  then 
heated  in  the  mantle  of  the  flame  near  the  apex  of  the  inner  cone,  and  the 
effect  observed. 

The  Bunsen  burner  consists  of  a  tube  having  at  its  base  a  series  of 
holes  to  admit  air,  and  also  a  small  gas  delivery  tube.  By  means  of 
this  contrivance  the  gas  is  mixed  with  air  before  it  burns  and  more 
perfect  oxidation,  and  consequently  much  greater  heat,  is  secured. 
Looking  attentively  at  the  flame  of  a  Bunsen  burner,  we  distinguish  in 
it  an  inner  part  and  two  mantles  surrounding  it.  The  inner  part 
corresponds  to  the  dark  nucleus  of  the  common  gas  flame,  and  con- 
tains the  mixture  of  gas  and  air  issuing  from  the  burner.  The  mantle 
immediately  surrounding  the  inner  part  contains  still  some  unconsumed 
carbide  of  hydrogen  ;  the  outer  mantle,  which  looks  bluer  and  less 
luminous,  consists  of  the  last  products  of  combustion.  The  Bunsen 
Fig 12C*  flame  is  illustrated  in  fig.  12  c.  In  it  u  o  and  L  o  are  respectively  the 
apper  and  lower  oxidising  flames,  and  u  R  and  L  R  the  upper  and  lower 


PREPARATION  OF  SULPHURETTED  HYDROGEN. 


reducing  ones,  z  F  is  the  zone  of  fusion  and  is  the  hottest  part,  having  a 
temperature  (according  to  Bunsen)  of  2,300°  C.  The  spot  where  the  reduc- 
ing action  is  the  most  powerful  and  energetic  lies  immediately  above  the  apex 
of  the  inner  part  of  the  flame.  The  Bunsen  flame  brings  out  the  coloration 
which  many  substances  impart  to  flames,  and  by  which  the  qualitative  analyst 
can  detect  many  bodies,  even  though  present  in  such  minute  quantities  that 
all  other  means  of  analysis  except  the  spectroscope  fail  to  discover  them. 
The  subject  of  the  coloration  of  flames  will  be  discussed  fully  under  eacv 
metal. 

XIII.   PREPARATION  OF  SULPHURETTED  HYDROGEN. 

This  is  done  by  acting  upon  ferrous  sulphide  with  dilute  sulphuric  acid. 
The  illustration  (fig.  13)  shows  the  apparatus.  The  ferrous  sulphide,  broken 
into  lumps  the  size  of  a  nut,  is  placed  in  the  generating  bottle  (A),  and 
dilute  sulphuric  acid  is  poured  in  by  the  funnel  (c)  in  small  quantities  as 
required.  B  is  a  bottle  containing  distilled  water,  through  which  the  gas 


Fig.  13. 


Fig.  14. 


Fig.  15- 


passes  to  free  it  from  any  traces  of  acid  mechanically  carried  over.  Owing  to 
the  disagreeable  odour,  it  is  desirable  to  have  special  appliances,  by  means  of 
which  the  evolution  of  the  gas  can  be  stopped  as  soon  as  it  has  done  the  work 
required.  Such  an  apparatus  for  use  in  a  large  laboratory  is  that  of  Kipps 
(fig.  14) ;  and  one  suitable  for  use  by  a  single  student  is  that  of  Van  Babo 
fig.  15).  Both  illustrations  sufficieatly  explain  themselves. 


CHAPTER   II, 

DETECTION  OF  THE  METALS. 

FOR  the  purposes  of  qualitative  analysis  we  employ  certain  chemicals,  either 
in  the  solid  or  liquid  state,  which  by  producing  given  effects  enable  us  to 
detect  the  existence  of  the  substance  searched  for.  These  substances  are 
always  kept  ready  for  use,  and  are  called  reagents.  They  are  of  three  classes : 
ist,  Group  reagents,  which,  by  yielding  a  precipitate  under  certain  condi- 
tions, prove  the  substance  to  be  a  member  of  a  certain  group  of  bodies ; 
2nd,  Separately  reagents,  by  means  of  which  the  substance  under  examination 
is  distinguished  from  the  other  members  of  the  group;  3rd,  Confirmatory 
reagents,  by  which  the  indications  previously  obtained  are  confirmed  and 
rendered  certain. 

The  Metals  are  divided  into  five  groups,   each  of  which   has   its  group 
reagent,  as  follows  : — 

GROUP  i.  Metals  the  chlorides  of  which,  being  insoluble  in  water,  are  precipi- 
tated from  their  solution  by  the  addition  of  hydrochloric  acid.  They 
are  silver,  mercurous  mercury,  and  lead  (the  latter  in  cold  strong 
solutions  only). 

GROUP  2.  Metals  the  sulphides  of  which,  being  insoluble  in  dilute  hydro- 
chloric acid,  are  precipitated  from  their  solutions  by  the  addition  of 
sulphuretted  hydrogen  in  the  presence  of  hydrochloric  acid.  This 
group  includes  mercury,  lead,  bismuth,  copper,  cadmium,  antimony, 
tin,  gold,  platinum,  and  the  metalloid  arsenic,  and  is  divided  into  two 
sub-groups,  as  follows  : — 

A.  Metals  the   sulphides   of  which  are   insoluble   in   both   dilute 
hydrochloric  acid  and  ammonium  sulphide.      The  precipitated  sul- 
phides separated  by  sulphuretted   hydrogen   are  therefore  insoluble, 
after   washing,  in   ammonium  sulphide.      They  are   mercury,   lead, 
bismuth,  copper,  and  cadmium. 

B.  Metals  the  sulphides  of  which,  although  insoluble  in  dilute  acids, 
are  dissolved  by  alkalies,  and  the  precipitates  from  their  solutions 
by  sulphuretted  hydrogen  therefore  dissolve  in  ammonium  sulphide. 
They  are  gold,  platinum,  tin,  antimony,  and  arsenic. 

GROUP  3.  Embraces  those  metals  the  sulphides  of  which  are  soluble  in  dilute 
acids,  but  are  insoluble  in  alkalies,  and  which  consequently,  having 
escaped  precipitation  in  Group  2,  are  now  in  turn  precipitated  by 
ammonium  sulphide.  They  are  iron,  nickel,  cobalt,  manganese,  and 
zinc.  In  this  group  are  likewise  included  aluminium,  cerium,  and 
chromium,  which  are  precipitated  as  hydrates  by  the  alkalinity  of  the 
ammonium  sulphide.  Magnesium  would  also  be  precipitated  as 
hydrate,  but,  as  that  would  be  inconvenient  at  this  stage,  its  precipi- 
tation is  prevented  by  the  addition  of  ammonium  chloride,  in  which 
its  hydrate  is  soluble. 


SILVER. 


GROUP  4.  Comprises  metals  the  chlorides  and  sulphides  of  which,  being 
soluble,  escape  precipitation  in  the  former  groups,  but  the  carbonates 
of  which,  being  insoluble  in  water,  are  now  precipitated  by  ammonium 
carbonate.  They  are  barium,  strontium,  and  calcium.  Magnesium 
is  not  precipitated  as  carbonate,  owing  to  the  presence  of  the  ammonium 
chloride  already  added  with  the  sulphide  in  Group  3. 

GROUP  5.  Includes  metals  the  chlorides,  sulphides,  and  carbonates  of  which, 
being  soluble  in  water  or  in  ammonium  chloride,  are  not  precipitated 
by  any  of  the  reagents  already  mentioned.     They  consist  of  magne- 
sium, lithium,  potassium,  sodium,  and  ammonium. 
As  the  analytical  grouping  of  the  metals  is  undoubtedly  one  which  is  most 

important  to  the  student   for  practical   purposes,  we   shall   adhere   to   this 

arrangement  in  giving  the  methods  for  their  detection. 

GROUP  I. 

Metals  precipitable  as  chlorides  by  the  addition  of  hydrochloric  acid  to 
their  solutions. 

I.   SILVER  (Ag). 

(a)    WET  REACTIONS. 

(To  be  practised  upon  a  solution  of  argentic  nitrate — AgNOs.) 

1.  Hydrogen  chloride  (hydrochloric  acid] — HC1  (ist  grcup  reagent]— or  any 

soluble  chloride  gives  a  curdy  white  precipitate  of  argentic  chloride — 
AgCl — insoluble  in  boiling  nitric  acid,  but  instantly  soluble  in  ammo- 
nium hydrate.  It  is  also  soluble  in  KCN,  Na.:S2O3,  and  in  strong 
solutions  of  soluble  chlorides. 

2.  Potassium   hydrate— KHO — or  sodium  hydrate—  NaHO — both  produce 

a  brownish  precipitate  of  argentic  oxide — Ag2O — insoluble  in  excess. 
A  similar  effect  is  produced  by  the  hydrates  of  barium,  strontium,  and 
calcium. 

3.  Potassium  chromate — K2Cr04— gives  a  red  precipitate  of  argentic  chromate 

— AggCrO* — soluble  in  large  excess  of  both  nitric  acid  and  ammonium 
hydrate  ;  and  therefore  the  solution  should  always  be  as  neutral  as 
possible. 

4.  Hydrogen  sulphide— H2S— and  ammonium  hydrogen  sulphide— NH4HS— 

both  produce  black  argentic  sulphide — Ag2S — insoluble  in  excess, 
both  soluble  in  strong  boiling  nitric  acid. 

5.  Potassium    iodide — KI— and    potassium    bromide — KBr — both   produce 

curdy  precipitates,  the  former  yellow  argentic  iodide — Agl — insoluble  in 
ammonium  hydrate,  and  the  latter  argentic  bromide — AgBr — dirty-white 
and  slowly  soluble  in  ammonium  hydrate. 

6.  Potassium   cyanide — KCN — gives   a  curdy-white    precipitate   of    argentic 

cyanide — AgCN — readily  soluble  in  excess,  and  also  in  boiling  strong 
nitric  acid. 

7.  Many  organic  salts,  such  as  formates  and  tartrates,  boiled  with  solutions  of 

silver,  precipitate  the  metal  as  a  mirror  on  the  tube. 

8.  Fragments  of  copper,  zinc,  iron,  and  tin,  introduced  into  a  solution  of 

silver,  all  precipitate  the  metal. 

(b)   DRY  REACTION. 
(To  be  practised  on  argentic  oxide — Ag2O.) 

Mixed  with  sodium  carbonate  and  heated  on  charcoal  before  the  blowpipe, 
a  bead  of  silver  is  formed,  hard,  glistening,  and  soluble  in  nitric  acid,  yielding 
solution  of  argentic  nitrate  to  which  the  wet  tests  may  be  applied. 


12  DETECTION  OF  THE  METALS. 

II.    MERCUROSUM    (Eg)*. 
(a)    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  mercurous  nitrate — Hg  (NO3)  prepared  by 
acting  upon  a  globule  of  mercury  with  cold  and  dilute  nitric  acid.) 

£.  BC1  (\st  group  reagent)  gives  a  white  precipitate  of  mercurous  chloride, — 
HgCl — turned  to  black  di-mercurous-ammonium  chloride — NH2Hg2Cl 
— by  ammonium  hydrate.  It  is  also  insoluble  in  boiling  water,  but 
soluble  in  strong  nitric  acid,  being  converted  into  a  mixture  of  mercuric 
chloride — HgCl2 — and  mercuric  nitrate — Hg(NO3)2. 

2.  KHO  and  NaHO  both  give  black  precipitates  of  mercurous  oxide — Hg2O — 

insoluble  in  excess. 

3.  Ammonium   hydrate — NH4HO — produces   a   black   precipitate   of  dimer- 

curous-ammonium  nitrate — NH2Hg2NO3H.,O — also  insoluble  in  excess. 

4.  Stannous  chloride —  SnCl2 — boiled  with  the  solution  causes  a  grey  precipitate 

of  finely  divided  mercury,  which,  if  allowed  to  settle,  and  then  boiled 
with  hydrochloric  acid  and  some  more  stannous  chloride,  aggregates 
into  a  globule. 

5.  KI  gives  a  green  precipitate  of  mercurous  iodide—  Hgl. 

(b)  DRY  REACTION. 
(To  be  tried  upon  mercurous  iodide.) 

Mercurous  compounds  when  heated  first  break  up  into  the  corresponding 
mercuric  salt  and  metallic  mercury,  and  finally  sublime  unchanged. 

III.   LEAD  (Pb). 

(a)    WET  REACTIONS. 
(To  be  practised  on  a  solution  of  plumbic  acetate — Pb(C2H3O2)2.) 

1.  HC1  (ist group  reagent)  forms  in  cold  strong  solutions  a  white  precipitate 

of  plumbic  chloride — PbCl2 — soluble  in  boiling  water. 

2.  H.,8  after  acidulation  by  HC1  (2nd  group  reagent)  gives  a  black  precipitate 

of  plumbic  sulphide — PbS— insoluble  in  ammonium  sulphide.  By 
treatment  with  boiling  strong  nitric  acid  it  is  decomposed,  partly  into 
plumbic  nitrate,  but  chiefly  into  insoluble  plumbic  sulphate.  It  is 
entirely  dissolved  by  hot  dilute  nitric  acid  with  separation  of  sulphur. 

3.  Hydrogen  sulphate  (sulphuric  acitf)—TSL$Qi — gives  a  white  precipitate  of 

plumbic  sulphate — PbSC>4 — slightly  soluble  in  water,  but  rendered 
entirely  insoluble  by  the  addition  of  a  little  alcohol.  It  is  decomposed 
by  boiling  strong  hydrochloric  acid,  and  is  also  freely  soluble  in 
solutions  of  ammonium  acetate  or  tartrate,  containing  an  excess  of 
ammonium  hydrate. 

4.  K2Cr04  gives  a  yellow  precipitate  of  plumbic  chromate — PbCrO4 — insoluble 

in  acetic  and  very  dilute  nitric  acids,  but  soluble  in  strong  boiling 
nitric  acid. 

5.  KI  gives  a  yellow  precipitate  of  plumbic  iodide — PbI2 — soluble  in  33  parts 

of  boiling  water,  and  crystallising  out  on  cooling  in  golden  scales. 

6.  KHO  and  NaHO  both  cause  white  precipitates  of  plumbic  oxy-hydrate — 

(PbO)2  Pb(HO)2 — soluble  in  excess,  forming  potassium  or  sodium 
plumbates— K2PbO2  and  Na2PbO2. 

7.  NH,HO  causes  a  white  precipitate  of  a  white  basic  nitrate — Pb(NO3HO)— 

insoluble  in  excess. 

8.  KCN  produces  a  white  precipitate  of  plumbic  cyanide — Pb(CN)2 — insoluble 

in  excess,  but  soluble  in  dilute  nitric  acid. 


MERCURICUM.  13 


9.  Alkaline  Carbonates  cause  a  precipitate  of  (PbCOa^PMHO),— • "  white 

lead  " — insoluble  in  excess,  and  also  in  potassium  cyanide. 
10.  Fragments  of  zinc  or  iron  in  the  presence  of  a  little  acetic  acid  cause  the 
separation  of  metallic  lead  in  crystalline  laminae. 

(b)  DRY  REACTION. 
(To  be  practised  on  red  lead — Pb3O4,  or  litharge — PbO.) 

Heated  on  charcoal  in  the  inner  blowpipe  flame,  a  bead  of  metallic  lead  is 
formed,  which  is  soft  and  malleable,  and  soluble  in  dilute  nitric  acid.  The 
solution  thus  obtained  gives  the  wet  tests  for  lead. 

GROUP  II. 

Metals  which  are  not  affected  by  acidulation  with  hydrochloric  acid,  but  are 
precipitated  by  passing  sulphuretted  hydrogen  through  the  acidulated  solution. 

DIVISION   A. 

Metals  which,  when  precipitated  by  sulphuretted  hydrogen  as  above,  yield 
sulphides  insoluble  in  ammonium  sulphide. 

I.  MERCURICUM  (Hg)." 

(a]    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  mercuric  chloride — HgCl2.) 

1.  H2S  after  acidulation  by  HC1  (2nd  group  reagent)  gives  a  black  precipitate 

of  mercuric  sulphide — HgS — insoluble  in  ammonium  sulphide  and 
nitric  acid,  and  only  soluble  in  nitro-hydrochloric  acid.  Care  must  be 
taken  that  the  sulphuretted  hydrogen  is  passed  really  in  excess,  and 
that  the  whole  is  warmed  gently,  as  unless  this  be  done,  the  precipitate 
is  not  the  true  sulphide,  but  a  yellowish-brown  dimercuric  sulpho- 
dichloride — Hg2SCl2.  Although  insoluble  in  any  single  acid,  mercuric 
sulphide  may  be  caused  to  dissolve  in  hydrochloric  acid  by  the  addition 
of  a  crystal  of  potassium  chlorate. 

2.  KHO  or  NaHO  both  give  a  yellow  precipitate  of  mercuric  oxide — HgO — 

insoluble  in  excess. 

3.  NH4HO  produces  a  white  precipitate  of  an  insoluble  mercuric-ammonium 

chloride — (NH2Hg)Cl — also  insoluble  in  excess. 

4.  KI  yields  a  red  precipitate  of  mercuric  iodide,  soluble  in  excess  both  of 

the  precipitant  and  the  mercuric  salt. 

5.  SnCl2,  boiled  with  a  mercuric  solution,  first  precipitates  mercurous  chloride, 

and  then  forms  metallic  mercury,  as  in  the  case  of  mercurosum 
compounds. 

6.  Alkaline  Carbonates  (except  ammonium  carbonate)  produce  an  immediate 

reddish-brown  precipitate  of  mercuric  oxy-carbonate. 

7.  Fragments  of  Cu,  Zn,  or  Fe  precipitate  metallic  mercury  in  the  presence 

of  dilute  hydrochloric  acid. 

(V)  DR  Y  REACTION. 
(To  be  tried  on  mercuric  oxide — HgO — and  on  "  Ethiops  mineral  " — HgS. ) 

All  compounds  of  mercury  are  volatile  by  heat ;  the  oxide  breaking  up  into 
oxygen  and  mercury,  which  sublimes,  while  the  sulphide  sublimes  unaltered 
unless  previously  mixed  with  sodium  carbonate  or  some  reducing  agent. 


1 4  DETECTION  OF  7 HE  METALS. 

II.  BISMUTH  (Bi). 
(a)    WET  REACTIONS. 

(To  be  practised  upon  bismuth  subnitrate^  dissolved  in  water  by  the  aid  of 
the  smallest  possible  quantity  of  nitric  acid,  and  any  excess  of  the  latter 
carefully  boiled  off.  This  solution  will  then  contain  bismuth  nitrate — 
Bi(N03)3. 

1.  H2S  after  addulation  by  HC1  (znd  group  reagent)  gives  a  black  precipitate 

of  bismuth  sulphide — Bi2S3 — insoluble  in  ammonium  sulphide,  but 
soluble  in  boiling  nitric  acid. 

2.  H2S04  gives  no  precipitate  (distinction  from  lead). 

3.  NH4HO,  KHO,  and  NaHO,  all  give  precipitates  of  white  bismuthous  hydrate 

Bi(HO)3 — insoluble  in  excess,  and  becoming  converted  into  the  yellow 
oxide — Bi2O3 — on  boiling. 

4.  Water — H20 — in  excess  to  a  solution  in  which  the  free  acid  has  been  as 

much  as  possible  driven  off  by  boiling,  gives  a  white  precipitate  of  a 
basic  salt  of  bismuth.  This  reaction  is  more  delicate  in  the  presence 
of  hydrochloric  than  of  nitric  acid  ;  and  the  precipitate,  which  is  in  this 
case  bismuth  oxy-chloride — BiOCl — is  insoluble  in  tartaric  acid  (dis- 
tinction from  antimonious  oxy-chloride). 

5.  K2Cr04  yields  a  yellow  precipitate  of  bismuth  oxy-chromate — Bi2O2CrO4 — 

soluble  in  dilute  nitric  acid,  but  not  in  potassium  hydrate  (distinction 
from  plumbic  chromate). 

6.  KI  gives  brown  bismuthous  iodide,  soluble  in  excess. 

7.  Alkaline   Carbonates  give  white   precipitates  of  bismuth  oxy-carbonate, 

insoluble  in  excess. 

8.  Fragments  of  zinc  added  to  a  solution  of  bismuth,  cause  a  deposit  of  the 

metal  as  a  dark  grey  powder. 

(If)  DRY  REACTION. 

(To  be  practised  upon  bismuth  sub  nit  rate.) 

Mixed  with  sodium  carbonate — Na2CO3 — and  heated  on  charcoal  before  the 
blowpipe,  a  hard  bead  of  metallic  bismuth  is  produced,  and  the  surrounding 
charcoal  is  incrusted  with  a  coating  of  oxide,  deep  orange-yellow  while  hot 
and  pale  yellow  on  cooling. 

III.  COPPER  (Cu.) 
(a)    WET  REACTIONS. 

(To  be  practised  with  a  solution  of  cupric  sulphate — CuSO4.) 

1.  H2S  after  addulation  with  HC1  (2nd  group  reagent)  forms  a  precipitate  of 

brownish-black  cupric  sulphide — CuS— which  is  nearly  insoluble  in 
ammonium  sulphide,  but  soluble  in  nitric  acid.  Its  precipitation  is 
prevented  by  the  presence  of  potassium  cyanide  (distinction  from 
cadmium).  When  long  exposed  to  the  air  in  a  moist  state,  it  oxidises 
to  cupric  sulphate  and  dissolves  spontaneously. 

2.  NH4HO  causes  a  pale  blue  precipitate  instantly  soluble  in  excess,  forming  a 

deep  blue  solution  of  tetrammonio-cupric  sulphate — (NH^CuSO^H^O. 

3.  Potassium  ferrocyanide — K4Fe(CN)6 — yields  a  chocolate-brown  precipitate 

of  cupric  ferrocyanide — Cu2Fe(CN)6.  This  test  is  very  delicate,  and 
is  not  affected  by  the  presence  of  a  dilute  acid,  but  does  not  take  place 
in  an  alkaline  liquid. 

4.  KHO  or  NaHO  precipitates  light-blue  cupric  hydrate — Cu(HO)2 — insoluble 

in  excess,  but  turning  to  black  cupric  oxy-hydrate — (CuO)2Cu(HO)2 — 
on  boiling. 


CA  DMIUM—A  RSENIC.  15 

5.  Potassium  sodium  tartrate  (Rochelle  salt}— KNaC4H406 — and  NaHO  added 

successively,  the  latter  in  excess,  produce  a  deep  blue  liquid  (Fehling's 
solution),  which,  when  boiled  with  a  solution  of  glucose  (grape  sugar) 
deposits  brick-red  cuprous  oxide — Cu2O. 

6.  The  Alkaline  Carbonates  precipitate  Cu(HO)2CuCO3. 

7.  Fragments   of  zinc   or   iron   precipitate   metallic  copper    from    solutions 

acidulated  with  HC1. 

(b)  DRY  REACTIONS. 
(To  be  practised  upon  cupric  oxide — CuO — or  verdigris — Cu2O(C2H3O2)2.) 

1.  Heated  with  Na2CO3  and  KCN  on  charcoal,  in  the  inner  blowpipe  flame, 

red  scales  of  copper  are  formed. 

2.  Heated  in  the  borax  bead  before  the  outer  blowpipe  flame,  colours  it  green 

while  hot  and  blue  on  cooling.  By  carefully  moistening  the  bead  with 
SnCl2  and  again  heating,  this  time  in  the  inner  flame,  a  red  colour  is 
produced. 

IV.   CADMIUM  (Cd). 

(a)    WET  REACTIONS. 
(To  be  practised  with  a  solution  of  cadmium  iodide — CdI2.) 

1.  H2S  after  aridulation  with  HC1  (2nd  group  reagent]  gives  a  yellow  precipi- 

tate of  cadmium  sulphide — CdS — insoluble  in  ammonium  sulphide, 
but  soluble  in  boiling  nitric  acid.  This  precipitate  does  not  form 
readily  in  presence  of  much  acid ;  but  its  production  is  not  hindered 
by  the  addition  of  potassium  cyanide  (distinction  from  copper). 

2.  NH4HO  produces  a  white  precipitate  of  cadmium  hydrate — Cd(HO)2 — 

soluble  in  excess. 

3.  KHO  or  NaHO  both  give  precipitates  of  cadmium  hydrate — Cd(HO)2 — 

insoluble  in  excess  (distinction  from  zinc). 

4.  Alkaline  Carbonates  precipitate  cadmium  carbonate — CdCOs — insoluble 

in  excess. 

(b)  DRY  REACTION. 

(To  be  practised  on  cadmium  carbonate— CdCO3.) 

Heated  on  charcoal  before  the  blowpipe,  a  brownish  incrustation  of  oxide 
is  produced,  owing  to  reduction  of  the  metal  and  its  subsequent  volatilisation 
and  oxidation  by  the  outer  flame. 

DIVISION  B. 

Metals  which  are  precipitated  by  sulphuretted  hydrogen  in  the  presence  of 
hydrochloric  acid,  but  yield  sulphides  which  are  soluble  in  ammonium  sulphide. 

I.   ARSENIC  (As). 
(a)    WET  REACTIONS. 

(To  be  practised  with  a  solution  of  arsenious  anhydride  in  boiling  water 
slightly  acidulated  by  hydrochloric  acid.) 

i.  HjS,  after  addulation  with  HC1,  causes-  a  yellow  precipitate  of  arsenious 
sulphide — As2Ss — soluble  in  ammonium  sulphide,  forming  ammonium 
sulpharsenite — (NH4)3AsS3 — but  insoluble  jn  strong  boiling  hydro- 
chloric acid  (distinction  from  the  sulphides  of  Sb  and  Sn).  This 
precipitate  is  also  soluble  in  cold  solution  Of  commercial  carbonate  of 
ammonia  (distinction  from  the  sulphides  of  Sb,  Sn,  Au,  and  Pt).  Dried 


16  DETECTION  OF  THE  METALS. 

and  heated  in  a  small  tube  with  a  mixture  of  Na,CO3  and  KCN,  it 
yields  a  mirror  of  arsenic.  (Detects  i  part  of  As  in  8000.) 

2.  Boiled  with  KH  0  and  a  fragment  of  Zinc,  arseniuretted  hydrogen — AsH3 — 

is  evolved,  which  stains  black  a  paper  moistened  with  solution  of 
argentic  nitrate  and  held  over  the  mouth  of  the  tube  during  the  ebul- 
lition (Fleitmanris  test). 

3.  Boiled  with  ^  of  its  bulk  of  HC1  and  a  slip  of  Copper,  a  grey  coating  is 

deposited  on  the  copper  of  cupric  arsenide.  On  drying  the  copper 
carefully,  cutting  it  into  fragments,  and  heating  in  a  wide  tube,  a 
crystalline  sublimate  of  arsenious  anhydride — As2O3 — 
is  obtained,  which,  when  examined  by  a  lens,  is  seen  to 
be  in  octohedral  crystals,  and,  when  dissolved  in  water, 
gives  a  yellow  precipitate  of  argentic  arsenite — Ag3As03 
— with  solution  of  ammonio-nitrate  of  silver  (Reinch's 
test).  (Detects  i  part  As  in  40,000.) 

4.  Placed   in  a  gas  bottle  furnished  with  a  jet  (illustrated  in 
the  margin),  together  with   dilute  sulphuric  or  hydro- 
chloric acid  and  a  few  fragments  of  zinc,  arseniuretted 
hydrogen — AsH3 — is   evolved,   which    may   be   lighted 
Flg" l6<  at  the  jet,  and  burns  with  a  lambent  flame,  producing 

As2O3.  If  a  piece  of  cold  porcelain  be  held  in  the  flame,  dark  spots  of 
arsenic  are  obtained,  readily  volatile  by  heat  and  soluble  in  solution 
of  chlorinated  lime  (Marsh's  test).  (Detects  i  part  As  in  200,000,000.) 

Note. — For  reactions  of  arsenites  and  arseniates,  see  Acid  Radicals. 

(V)  DRY  REACTION. 
(To  be  practised  on  arsenious  anhydride — As2O3.) 

Heated  in  a  small  tube  with  Na2COs  and  KCN,  a  mirror  of  arsenic  is  pro- 
duced, accompanied  by  a  garlic-like  odour.  The  same  effect  may  be  produced 
with  black  flux. 

II.  ANTIMONY  (Sb). 

(a)    WET  REACTIONS. 
(To  be  practised  with  a  solution  of  tartar  emetic  (K(SbO)C4H4O6)2.H,O.) 

1.  H;S,  after  acidulation  by  HC1,  causes  an  orange  precipitate  of  antimonious 

sulphide — Sb^Ss — soluble  in  ammonium  sulphide,  forming  ammonium 
sulphantimonite — (NH4)J5bS3 — also  soluble  in  strong  boiling  hydro- 
chloric acid,  forming  antimonious  chloride — SbCl3 — but  insoluble  in 
cold  solution  of  commercial  carbonate  of  ammonia. 

2.  KHO  and  NaHO  produce  precipitates  of  antimonious  oxide  readily  soluble 

in  excess  to  form  antimonites  (K3SbO3  or  NagSbOa). 

3.  Acidulated  with  HC1  and  introduced  into  a  platinum  dish  with  a  rod  of 

zinc  so  held  that  it  touches  the  platinum  outside  the  liquid,  a  black 
stain  of  metallic  antimony  is  produced  closely  adherent  to  the  platinum. 
This  stain  is  not  dissolved  by  HC1  (tin  reduced  in  the  same  manne 
is  granular  and  soluble  in  boiling  HC1). 

4.  Reinch's  test  (see  Arsenic)  produces  a  black  coating  on  the  copper,  which, 

when  heated,  forms  an  amorphous  sublimate  of  Sb2O3  dose  to  the  copper^ 
and  insoluble  in  water,  but  dissolved  by  a  solution  of  cream  of  tartar 
in  which  H2S  then  produces  the  characteristic  orange  sulphide. 

5.  Marsh's  test  (see  Arsenic)  yields  stains  of  antimony  on  the  porcelain,  not 

nearly  so  readily  volatile  by  heat  as  in  the  case  of  arsenic,  and  not 
discharged  by  solution  of  chlorinated  Hm?. 


TIN— GOLD.  ,7 


6.  Fleitmann's   test   will    not   act   with   antimony   at   all   (distinction    from 
arsenic). 

(b)  DRY  REACTION. 
(To  be  practised  on  antimonious  oxide — Sb2O3.) 

Heated  on  charcoal  with  Na2CO3  and  KCN  before  the  blowpipe,  a  bead 
of  metallic  antimony  is  formed  and  copious  white  fumes  of  the  oxide  are 
produced. 

III.   TIN  (Sn«  or  Sn"). 
(a)    WET    REACTIONS. 

(To  be  practised  with  a  solution  of  stannous  chloride — SnCl2 — and  one  of 
stannic  chloride — SnCU — prepared  by  warming  the  stannous  solution  with 
a  little  nitric  acid.) 

1.  H2S,  after  addulation  with  HC1,  produces  a  brown  or  yellow  precipitate 

of  SnS  or  SnS2  respectively,  both  soluble  in  ammonium  sulphide  and 
in  boiling  hydrochloric  acid. 

2.  KHO  or  NaHO  both  produce  white  precipitates  of  Sn(HO).2  or  Sn(HO)4, 

soluble  in  excess,  the  former  to  produce  stannites  and  the  latter  stan- 
nates.  The  stannous  solution  is,  however,  reprecipitable  on  boiling, 
while  the  stannic  is  not. 

3.  NH4HO  produces  similar  precipitates,  very  difficultly  soluble  in  excess. 

4.  Acidulated  by  HC1,  and  introduced  into  a  platinum  dish  with  a  rod  of 

zinc,  so  held  in  the  fluid  that  it  touches  the  platinum  outside  the  liquid, 
granules  of  metallic  tin  are  deposited,  soluble  in  boiling  HC1,  to  form 
stannous  chloride. 

5.  HgCl2  boiled  with  stannous  salts  deposits  a  grey  precipitate  of  metallic 

mercury. 

(b)  DRY  REACTION. 
(To  be  practised  on  putty  powder — SnOj.) 

Heated  on  charcoal  with  Na2CO3  before  the  blowpipe,  a  bead  of  metallic 
tin  is  produced,  and  a  white  incrustation  of  oxide  is  formed  on  the  charcoal. 

IV.  GOLD  (Au). 
(a)    WET   REACTIONS. 

(To  be  practised  with  a  solution  of  auric  chloride — AuCl3.) 

1.  HL,S  (group  reagent)  in  the  presence  of  HC1  gives  black  auric  sulphide 

— Au2S3.  If  the  solution  be  hot,  aurous  sulphide — Au2S — falls.  Both 
are  only  soluble  in  nitro-hydrochloric  acid,  but  they  are  soluble  in 
ammonium  sulphide  when  it  is  yellow. 

2.  NH4HO   precipitates    reddish   ammonium   aurate,    or  fulminating  gold — 

Au2(NH3)A,—  but  KHO  gives  no  result. 

3.  Hydrogen  oxalate   (oxalic  acid} — H2C204  (or  Ferrous  sulphate — FeS04) 

—when  boiled  with  an  acid  solution  throws  down  Au.  Reducing  agents 
generally  act  thus.  The  liquid  containing  the  metal  may  exhibit  a  blue, 
green,  purple,  or  brown  colour. 

4.  SnCl2  throws  down  a  brownish  or  purplish  precipitate  known  as  "  purple 

of  Cassius,"  consisting  of  the  mixed  oxides  of  gold  and  tin. 

5.  Zn,  Cu,  Fe,  Pt,  or  almost  any  metal,  gives  a  precipitate  of  metallic  Au  in 

a  finely  divided  state. 


f8  DETECTION  OF  THE  METALS. 

(b)  DRY  REACTION. 
(To  be  practised  on  any  gold  salt.) 
Heated  on  charcoal  with  Na2CO3,  the  metal  is  produced 

V.   PLATINUM  (Pt). 

(a)    WET  REACTIONS. 

(To  be  tested  with  a  solution  of  platinic  chloride — PtCl4.) 

t.  H2S  (2 nd group  reagent)  in  presence  of  HC1  gives  a  brown  precipitate  of 
platinic  sulphide— PtSo.  This  precipitate  forms  slowly,  and  is  readily 
dissolved  by  yellow  ammonium  sulphide. 

2.  Potassium  chloride — KC1 — in  presence  of  HC1,  especially  after  addition  of 

alcohol,  produces  a  yellow  crystalline  precipitate  of  potassium  platinic 
chloride — PtCl4(KCl)2—  soluble  to  a  moderate  extent  in  water,  but  not 
in  alcohol.  Decomposition  takes  place  when  this  is  strongly  heated, 
metallic  Pt  and  KC1  remaining. 

3.  Ammonium  chloride — NH4C1— gives  a  precipitate  of  ammonium  platinic 

chloride — PtCl4(NH4Cl)2 — which  is  almost  identical  in  properties,  but 
is  more  readily  decomposed  by  heat,  pure  platinum  remaining. 

4.  In,  Fe,  and  several  other  metals  decompose  platinic  salts  with  the  produc- 

tion of  the  metal. 

(b)  DRY  REACTIOA. 
(To  be  practised  upon  potassium  platinic  chloride — PtCl4(KCl)2.) 

Heat  on  charcoal,  with  or   without  Na2CO3,  before  the  blowpipe.     The 
«ietal  is  produced  by  reduction. 


GROUP  III. 

Metals  which  escape  precipitation  by  sulphuretted  hydrogen  in  presence 
of  hydrochloric  acid,  but  which  are  precipitated  by  ammonium  sulphide  in  the 
presence  of  ammonium  hydrate,  ammonium  chloride  having  been  previously 
added  to  prevent  the  precipitation  of  magnesium. 

DIVISION   A. 

Metals  which,  in  the  insured  absence  of  organic  matter,  are  precipitated  as 
•hydrates  by  the  addition  of  the  ammonium  chloride  and  ammonium  hydrate 
•only. 

I.    IRON  (Ferrous,  Fe ;  and  Ferric,  Fe2). 
(a)    WET  REACTIONS. 

<To  be  practised  successively  on  solutions  of  ferrous  sulphate — P\'SO4 — and 

ferric  chloride — Fe2Cl6-) 

•t.  NH4HO  in  the  presence  of  NH4C1  (group  reagent]  yields  either  a  dirty- 
green  precipitate  of  ferrous  hydrate — Fe(HO)2 — or  a  reddish  brown 
precipitate  of  ferric  hydrate — Fe,(HO)6.  The  former  is  slightly  soluble 
in  excess,  but  the  latter  is  insoluble,  and  it  is  therefore  preferable 
always  to  warm  the  solution  with  a  little  nitric  acid,  to  insure  the 
laising  of  the  iron  to  the  ferric  state,  before  adding  the  ammonium 
hydrate.  The  presence  of  organic  acids,  such  as  tartaric  or  citric, 


IRON.  19 


prevents  the  occurrence  of  this  reaction ;  and  therefore,  if  any  such 
admixture  be  suspected,  the  solution  should  first  be  evaporated  to  dry- 
ness,  the  residue  heated  to  redness,  and  then  dissolved  in  a  little 
hydrochloric  acid,  heated  with  a  drop  or  two  of  nitric  acid,  diluted, 
and  lastly,  the  NH4C1  and  NH4HO  added  and  boiled. 

a.  NH4HS  added  to  a  neutral  or  alkaline  solution,  produces  a  precipitate 
of  ferrous  sulphide — FeS— which  is  black  (distinction  from  Al,  Ce, 
Cr,  Mn,  and  Zn),  and  readily  soluble  in  cold  diluted  hydrochloric 
acid  (distinction  from  the  black  sulphides  of  Ni  and  Co).  This  re- 
action takes  place  even  in  the  presence  of  organic  matter,  and  the 
precipitated  sulphide,  if  exposed  to  the  air,  gradually  oxidises  to  fer- 
rous sulphate — FeSO4 — and  disappears.  It  is  insoluble  in  acetic  acid 
(distinction  from  MnS). 

3.  K4Fe(CN)6,  in  a  neutral  or  slightly  acid  solution,  gives,  with  ferrous  salts,  a 

white  precipitate  (rapidly  changing  to  pale  blue)  of  Everett's  salt — potas- 
sium ferrous  ferrocyanide — K2Fe .  Fe(CN)6 — and  with  ferric  salts,  a  dark 
blue  precipitate  of  Prussian  blue — ferric  ferrocyanide  (Fe2)2(Fe(CN)6)3. 
These  precipitates  are  decomposed  by  alkalies,  producing  the  hydrates 
of  iron,  and  forming  a  ferrocyanide  of  the  alkali  in  solution  ;  but  the 
addition  of  hydrochloric  acid  causes  the  re-formation  of  the  original 
precipitate. 

4.  Potassium  ferricyanide — K6Fe2(CN)12 — gives,  with  ferrous  salts,  in  neutral 

or  slightly  acid  solutions,  a  dark  blue  precipitate  of  TurnbulPs  blue — 
ferrous  ferricyanide,  Fe3Fe2(CN)12 — but  with  ferric  salts  it  gives  no 
precipitate,  simply  producing  a  brownish  liquid.  With  alkalies, 
Turnbull's  blue  is  decomposed,  yielding  black  ferroso-ferric  hydrate, 
and  a  ferricyanide  of  the  alkali ;  but  the  addition  of  hydrochloric  acid 
reproduces  the  original  blue. 

5.  Potassium  thiocyanate  (sulphocyanate) — KCNS — gives  no  precipitate  with 

ferrous  salts,  but  with  ferric  compounds  it  yields  a  deep  blood-red 
solution.  This  colour  is  not  discharged  by  dilute  hydrochloric  acid 
(distinction  from  ferric  acetate),  but  immediately  bleached  by  solution 
of  mercuric  chloride  (distinction  from  ferric  meconate). 

6.  KHO,  or  NaHO,  produces  effects  similar  to  those  of  ammonium  hydrate. 

7 .  Oisodium  phosphate— Na,HP04—/^  the  presence  of  NaC2H302  or  NH4C2Ho02 

— gives  a  whitish  gelatinous  precipitate  of  ferrous  or  ferric  phosphates — 
Fe8(PO4)2  or  Fe^(PO4)2 — insoluble  in  acetic  acid,  but  soluble  in  hydro- 
chloric acid.  The  previous  addition  of  citric  or  tartaric  acids  prevents 
this  reaction. 

8.  Sodium  acetate — NaC2H302 — added  in  excess  to  ferric  salts,  produces  a  deep 

red  solution  of  ferric  acetate — Fe2(CoH3O2)6 — which  on  boiling  deposits 
as  a  reddish -brown  ferric  oxyacetate — FesCXCgHsO^.  This  precipi- 
tate dissolves  slightly  on  cooling  ;  but  iron  can  be  entirely  precipitated 
in  this  form  if  the  solution  be  instantly  filtered  while  hot. 

9.  Alkaline  Carbonates,  added  to  a  ferrous  salt,  precipitate  white  ferrous 

carbonate — FeCOs — but  with  ferric  salts  throw  down  the  reddish-brown 
ferric  hydrate  already  described. 

(b)  DRY  REACTIONS. 
(To  be  practised  on  ferric  oxide.) 

1.  Heated  on  charcoal  before  the  inner  llowpipe  flame,  a  black  magnetic 

powder  is  obtained,  which  is  not  the  rmtal,  but  is  ferroso-ferric  oxide 
-Fe3O4. 

2.  Heated  in  the  borax  bead  in  the  inner  blowpipe  flame,  a  bottle-green 


DETECTION  OF  THE  METALS. 


colour  is  produced ;  but  in  the  outer  flame  the  bead  is  deep  red  while 
hot,  and  very  pale  yellow  when  cold. 

H.  CERIUM  (Ce). 
(a)    WET   RE 'ACTIONS. 

(To  he  practised  on  cerous  chloride — CeCl3— prepared  by  boiling  cerium 
oxalate  with  sodium  hydrate,  washing  the  insoluble  cerous  hydrate  with 
boiling  water,  and  dissolving  it  in  the  least  possible  excess  of  hydrochloric 
acid.) 

1.  NH4HO  in  the  presence  of  NH4C1  (gtoup  reagent)  gives  a  white  precipitate 

of  cerous  hydrate — Ce(HO)6 — insoluble  in  excess. 

2.  KHO  and  NaHO  give  a  similar  precipitate,  turning  yellow  on  the  addition 

of  chlorine  water. 

3.  Ammonium    oxalate    gives    a    white    precipitate    of    cerous    oxalate— 

Ce2(C2O4)32H2O — insoluble  in  excess,  and  not  readily  dissolved  even 
by  hydrochloric  acid.  The  presence  of  citric  or  tartaric  acid  does  not 
interfere  with  this  reaction. 

4.  Potassium  sulphate — K2S04 — in  a  saturated  solution  causes  the  formation 

of  white  crystalline  potassium  cerium  sulphate — K2SO4Ce2(SO4)3 — 
soluble  in  hot  water. 

(b)  DRY  REACTIONS. 
(To  be  practised  on  cerium  oxalate.) 

I.  Heated  to  redness  in  contact  with  the  air,  an  orange  red  residue  of  eerie 
oxide — CeO2 — is  obtained,  difficultly  soluble  even  in  strong  hydro- 
chloric acid. 

a.  Heated  in  the  borax  bead,  cerium  behaves  like  iron  in  the  outer  flame, 
but  the  inner  flame  yields  a  colourless  or  opaque  yellow  bead. 

Til.   ALUMINIUM  (Al). 
(a)   WET  REACTIONS. 

(To  be  practised  on  a  solution  of  common  alum.) 

1.  NH4HO  in  presence  <7/"NH4Cl  (group  reagent)  gives  a  gelatinous  white  pre- 

cipitate of  aluminic  hydrate — A12(HO)6.  This  precipitate  is  slightly 
soluble  in  a  large  excess  of  the  precipitant,  but  separates  completely 
on  boiling. 

2.  KHO  and  NaHO   both  give  a  similar  precipitate,  soluble  in  excess,   but 

reprecipitated  by  boiling  with  an  excess  of  ammonium  chloride,  or  by 
neutralising  with  hydrochloric  acid  and  boiling  with  a  slight  excess 
of  ammonium  hydrate. 

3.  Na.,HP04  in    the  presence  of  NaC2H3O2   or    NH4C2HaO2   gives   a    white 

precipitate  of  aluminic  phosphate — A1PO4 — insoluble  in  hot  acetic 
acid,  but  soluble  in  hydrochloric  acid.  The  presence  of  citric  or 
tartaric  acids  prevents  the  occurrence  of  this  reaction. 

(b)  DRY  REACTION. 
(To  be  practised  on  dried  alum.) 

Heat  stronglv  on  charcoal  before  the  blowpipe,  when  a  strong  incandescence 
is  observed,  and  a  white  residue  is  left.  Moisten  this  residue  with  a  drop  of 
solution  of  cobaltous  nitrate — Co(NO3)2 — and  again  heat  strongly,  when  a 
blue  mass  is  left.  This  test  is  not  decisively  characteristic,  as  other  substances, 
such  as  zinc  and  earthy  phosphates,  show  somewhat  similar  colours. 


CHROMIUM— MANGANESE.  21 

IV.   CHROMIUM  (Cr). 
(a)    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  potassium  chromic  chloride,  prepared  by 
dissolving  potassium  dichromate — K2Cr2O7 — in  water,  acidulating  with 
hydrochloric  acid,  heating  and  dropping  in  alcohol  till  the  solution  turns 

green.) 

1.  NH4HO  in  the  presence  ^/rNH4Cl  (group  reagent]  precipitates  green  chromic 

hydrate — Cr2(HO)6 — slightly  soluble  in  excess,  but  entirely  re  precipi- 
tated on  boiling.  The  presence  of  citric  or  tartaric  acid  interferes 
with  the  completeness  of  this  reaction. 

2.  KHO,  or  NaHO,  gives  similar  precipitates,  freely  soluble  in  excess  when 

cold,  but  entirely  reprecipitable  by  continued  boiling. 

3.  Chlorinated  soda— Na2OCl2 — or  Plumbic  peroxide — Pb62 — boiled  with  an 

alkaline  solution  of  a  chromium  salt,  produces  a  yellow  solution  of 
sodium  chromate — Na2CrO4. 

4.  NaHP04  in  the  presence   of  NaC2H302  or  NH4C2H302  throws   down  pale 

green  chromic  phosphate — CrPO4 — soluble  when  freshly  precipitated 
in  excess  of  hot  acetic  acid,  and  freely  soluble  in  hydrochloric  acid. 
The  presence  of  organic  acids  prevents  this  reaction. 

(V)  DRY  REACTIONS. 

1.  Heated  in  the   borax   bead  in  the  inner  blowpipe  flame,  a  fine  green 

colour  is  obtained. 

2.  Fused  on  platinum  foil,  with  a  mixture  of  KNaCO3  and  KNO3,  a  yellow 

residue  is  obtained,  consisting  of  chromates  of  the  alkalies  used. 
This  mass  is  soluble  in  water,  yielding  a  yellow  solution  turned  deeper 
in  colour  by  the  addition  of  hydrochloric  acid,  owing  to  the  formaiion 
of  dichromates,  and  becoming  green  on  warming  and  dropping  in 
rectified  spirit. 

DIVISION    B. 

Metals  the  hydrates  of  which,  being  soluble  in  excess  of  ammonium  hydrate 
in  the  presence  of  ammonium  chloride,  escape  precipitation  by  that  reagent, 
but  are  separated  as  insoluble  sulphides  by  the  addition  of  ammonium  sulphide 
to  the  same  liquid. 

I.   MANGANESE  (Mn). 
(a)    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  potassium  manganous  chloride,  prepared  by 
heating  a  solution  of  potassium  permanganate  with  hydrochloric  acid,  and 
dropping  in  alcohol  until  a  colourless  solution  is  obtained.) 

i.  NH4HS  in  the  presence  of  NH4C1  and  NH4HO  (group  reagent)  precipitates 
a  flesh-coloured  manganous  sulphide — MnS — soluble  in  dilute  and 
cold  hydrochloric  acid  (distinction  from  the  sulphides  of  Ni  and 
Co).  It  is  also  soluble  in  acetic  acid  (distinction  from  zinc  sulphide). 
This  precipitate  forms  sometimes  very  slowly  and  only  after  gently 
warming.  If  a  good  excess  of  NH4C1  has  not  been  added,  or  if,  after 
adding  the  excess  of  ammonium  hydrate,  the  solution  be  exposed  lo 
the  air,  a  portion  of  the  manganese  will  sometimes  precipitate  sponta- 
neously, as  manganic  dioxyhydrate — Mn,O,(HO)| — and  be  found  with 
the  iron,  etc.,  in  the  first  division  of  the  thi'd  ^roup.  In  this  case  its 


22  DETECTION  OF  THE  ME1ALS. 

presence  will  be  easily  made  manifest  during  the  fusion  for  chromium 
by  the  residue  being  green.  It  is  therefore  evident  that  small  quan- 
tities of  manganese  cannot  be  perfectly  separated  from  large  quantities 
of  iron  by  NH4C1  and  NH4HO  only. 

2.  KHO  and  NaHO  both  yield  precipitates  of  manganous  hydrate  insoluble 

in  excess,  and  converted  by  boiling  into  dark  brown  manganic  dioxy- 
hydrate— Mn2O2(HO),. 

3.  NH4HO  gives  a  similar  precipitate,  soluble  in  excess  of  ammonium  chloride, 

but  gradually  depositing  as  Mn2O2(HO)2  by  exposure  to  tha  air.  For 
this  reason,  if  the  presence  of  manganese  be  suspected,  the  addition 
of  NH4C1  and  NH4HO  must  be  followed  by  instant  filtration,  and  any 
cloudiness  coming  in  the  filtrate  must  be  simply  taken  as  indicating 
manganese,  and  disregarded. 

4.  K4Fe(CN)g  gives  a  precipitate  of  manganous  ferrocyanide — Mn2Fe(CN)6 — 

very  liable  to  be  mistaken  for  the  corresponding  zinc  compound. 

5.  Boiled  with  plumbic  peroxide  and  nitric  acid  a  violet  colour  is  produced  in 

the  liquid,  due  to  the  formation  of  permanganic  acid.     (Crum's  test.) 

(b)  DRV  REACTIONS. 
(To  be  practised  upon  manganese  peroxide  — MnO2.) 

1.  Fused  on  platinum  foil  with  KHO  and  a  crystal  of  KC1O3,  a  green  mass 

of  potassium  manganate  is  formed.  This  residue  is  soluble  in  water, 
yielding  a  green  solution,  turning  purple  on  boiling,  owing  to  the 
formation  of  potassium  permanganate.  The  solution  is  rendered 
colourless  by  heating  with  hydrochloric  acid  and  dropping  in  alcohol, 
the  operation  being  accompanied  by  the  odour  of  aldehyd. 

2.  Healed  in  the  borax  bead  in  the  outer  blowpipe  flame,  a  colour  is  produced 

which  is  violet-red  while  hot  and  amethyst  on  cooling.  The  bead  is 
rendered  colourless  by  the  reducing  flame. 

II.  ZINC  (Zn). 

(a)  WET  REACTIONS. 

(To  be  practised  on  zinc  sulphate — ZnSO4.) 

1.  NH4HS  in  the  presence  0/"NH4Cl  and  NH4HO  (group  reagent)  gives  a  white 

precipitate  of  zinc  sulphide — ZnS — insoluble  in  acetic  acid,  but  readily 
soluble  in  dilute  hydrochloric  acid. 

2.  KHO,  NaHO,  and  NH4HO,  all  give  precipitates  of  gelatinous  white  zinc 

hydrate,  soluble  in  excess  to  form  zincates.  The  addition  of  sulphu- 
retted hydrogen  or  ammonium  sulphide  reprecipitates  the  zinc  as  zinc 
sulphide — ZnS. 

3.  K4Fe(CN)6  gives  a   gelatinous   white   precipitate    of  zinc   ferrocyanide— 

Zn.2Fe(CN)6 — insoluble  in  dilute  acids. 

4.  Alkaline    Carbonates    precipitate    ZnCO,(Zn2HO)2H2O— zinc    hydrato- 

carbonate — insoluble  in  excess  of  the  carbonates  of  potassium  and 
sodium,  but  soluble  in  that  of  ammonium.  The  latter  solution,  diluted 
and  boiled,  deposits  the  oxide. 

(b)  DRY  REACTIONS. 
(To  be  practised  on  zinc  carbonate.) 

I.  Salts   of  zinc  heated  leave   the  oxide,  yellow  while  hot,  and  white  on 
coolinr. 


NICKEL— COBALT.  23, 


2.  Heated  on  charcoal  before  the  blowpipe  an  incrustation  forms,  yellow 
while  hot,  and  white  on  cooling.  Moisten  with  a  drop  of  cobaltous 
nitrate— Co(NO3)2 — and  again  heat  it  in  the  outer  flame,  when  a  fine 
green  colour  is  produced. 

III.  NICKEL  (Ni). 

(a)  WET  REACTIONS. 

(To  be  practised  on  a  solution  of  nickelous  sulphate — NiSO4.) 

1.  NH4HS  in  the  presence  of  NH4C1  and  NH4HO  (group  reagent}  gives  a  black 

precipitate  of  nickelous  sulphide — NiS — slightly  soluble  in  excess,  but 
entirely  precipitated  on  boiling.  It  is  not  soluble  in  cold  dilute 
hydrochloric  or  in  acetic  acid,  but  requires  boiling  with  strong- 
hydrochloric  acid,  and  sometimes  even  the  addition  of  a  drop  or  two* 
of  nitric  acid. 

2.  KHO  or  NaHO  both   give   a   green   precipitate   of  nickelous   hydrate — 

Ni(HO)2 — unaltered  by  boiling  (distinction  from  cobalt). 

3.  Potassium  nitrite— KN02 — added  to  a  neutral  solution,  followed  by  an 

excess  of  acetic  acid,  gives  no  precipitate  (after  standing  some  hours) 
on  the  addition  of  potassium  acetate  and  rectified  spirit  (very  useful 
separation  from  cobalt). 

4.  KCN  in  excess  produces  a  greenish-yellow  precipitate  of  nickelous  cyanide: 

— Ni(CN)2 — which  quickly  redissolves.  On  adding  a  drop  of  hydro- 
chloric acid  and  boiling  in  a  fume  chamber,  and  repeating  this  till  no ' 
more  fumes  of  hydrocyanic  acid  come  off,  and  then  adding  sodium, 
hydrate,  a  precipitate  of  nickel  hydrate  is  produced.  It  is  better,, 
although  less  convenient,  to  use  a  strong  solution  of  chlorinated  soda> 
instead  of  HC1,  when  nickelic  hydrate — Ni(HO)6 — is  slowly  precipitated 
(separation  from  Co,  which  gives  no  precipitate). 

5.  Alkaline  Carbonates  behave,  so  far  as  colour  and  solubility  in  excess  are 

concerned,  like  their  respective  hydrates. 

(b)  DR  Y  REACTIONS. 

1.  Heated  on  charcoal  with  Na2CO3  in  the  inner  blowpipe  flame,  a  grey- 

metallic  and  magnetic  powder  is  produced. 

2.  Heated  in  the  borax  bead  in  the  outer  blowpipe  flame,  red  to  violet-brown  • 

is   produced  while  hot,    and   a   yellowish   to   sherry-red    when    cold. 
These  colours  might  be  mistaken  for  those  of  iron ;  but  on  fusing  a< 
small  fragment  of  potassium  nitrate  with  the  bead,  its  colour  at  once.- 
changes  to  blue  or  dark  purple  (distinction  from  Fe). 

IV.  COBALT  (Co). 

(a)   WET  REACTIONS. 

(To  be  practised  on  a  solution  of  cobaltous  nitrate— Co(NO3)2.) 

1.  NH4HS  in  the  presence  of  NH4C1  and  NHtHO  (group  reagent]  gives  a  black 

precipitate  of  cobaltous  sulphide — CoS — insoluble  in  acetic  and  cold 
dilute  hydrochloric  acid,  and  requiring  to  be  boiled  with  the  strongest 
HC1,  often  with  the  addition  of  a  drop  or  two  of  nitric  acid  before 
solution  is  effected. 

2.  KHO,  or  NaHO,  gives  a  blue  precipitate,  which  rapidly  changes  on  boiling; 

to  pink  cobaltous  hydrate — Co(HO)2 — (distinction  from  nickel). 

3.  KCN  gives  a  light  brown  precipitate  of  cobaltous  cvanide,  raoidlv  soluWc 


DETECTION  OF  THE  METALS. 


in  excess,  but  reprecipitated  by  excess  of  dilute  hydrochloric  acid.  If, 
however,  the  HC1  be  added  drop  by  drop  just  so  long  as  it  causes 
the  evolution  of  hydrocyanic  acid  fumes  on  boiling,*  soluble  potassium 
cobalticyanide — K6CCX(CN)12 — results,  which  is  not  decomposed  by 
hydrochloric  acid;  nor  is  any  precipitate  produced  on  adding  excess 
of  sodium  hydrate  or  chlorinated  soda  (separation  from  nickel). 
4.  Alkaline  Carbonates  throw  down  basic  carbonates,  behaving  like  the 
respective  hydrates. 

(b)  DRY  REACTIONS, 

1.  Heated  on  charcoal  with  Na2COs  in  the  inner  blowpipe  flame,  the  cobalt 

separates  as  a  grey  magnetic  powder. 

2.  Heated  in  the  borax  bead,  first  in  the  outer  and  then  in  the  inner  flame, 

a  fine  blue  colour  is  produced.  It  is  an  important  distinction  of  cobalt 
from  copper,  manganese,  etc.,  that  prolonged  heating  in  the  inner  flatne 
does  not  affect  this  blue. 


GROUP  IV. 

Metals  the  hydrates  and  sulphides  of  which,  being  soluble,  are  not  precipi- 
tated by  the  addition  of  NH4HO  and  NH4HS  in  the  presence  of  NH4C1, 
but  separate  as  insoluble  carbonates  on  the  addition  of  ammonium  carbonate 
to  the  same  solution. 

I.   BARIUM  (Ba). 

(a)    WET  REACTIONS. 
(To  be  practised  on  a  solution  of  barium  chloride  —  BaClj.) 


1.  Ammonium  carbonate  —  (NH4)2C03  —  in  the  presence  ^NH^Cl 

(group  reagent)   produces  a  white  precipitate  of  barium  carbonate  — 
BaCO3  —  soluble  with  effervescence  in  dilute  acetic  acid. 

2.  H2S04  and  all  soluble  Sulphates  give  a  white  precipitate  of  barium  sul- 

phate —  BaSO4  —  insoluble  in  ammonium  acetate  or  tartrate  (distinction 
from  PbSO4)  and  also  in  boiling  nitric  acid. 

3.  K1Cr04  gives  a  yellow  precipitate  of  barium  chfomate  —  BaCrO4  —  insoluble 

in  water  and  in  dilute  acetic  acid,  but  soluble  in  hydrochloric  acid 
(distinction  from  Sr  and  Ca). 

4.  (NH4)2C204  gives  a   white    precipitate   of  barium    oxalate  —  BaC2O4  —  not 

readily  formed  in  the  presence  of  much  acetic  acid. 

5.  NaiHP04    gives   a   white    precipitate    of   barium    hydrogen    phosphate  — 

BaHPO4  —  soluble  in  acetic  acid,  and  to  some  extent  in  ammonium 
chloride. 

(b)  DRY  REACTION. 
(To  be  practised  also  on  barium  chloride.) 

If  a  platinum  wire  be  dipped  first  in  hydrochloric  acid  and  then  in  the  salt, 
and  held  in  the  inner  blowpipe  or  Bunsen  flame,  the  outer  flame  is  coloured 
yellowish-green. 

*  This  must  be  done  in  a  fume  chamber,  as  it  is  a  highly  poisonous  operation  if  the  fumes 
nhould  happen  to  escape  into  the  room. 


STRONTIUM— CALCIUM.  25 

II.    STRONTIUM  (Sr). 

(a)    WET  REACTIONS. 

(To  be  practised  on  strontium  nitrate — Sr(NO3)2-) 

1  (NH4)2C03  (group  reagent]  in  the  presence  of  NH4C1   and  NH4HO   gives 

a  white  precipitate  of  strontium  carbonate — SrCO3 — soluble  in  dilute 
acetic  acid. 

2  H2S04,  or  a  soluble  sulphate  (preferably  calcium  sulphate),  yields  a  white 

precipitate  of  strontium  sulphate — SrSO4 — which  only  separates  com- 
pletely from  dilute  solutions  on  allowing  them  to  stand  in  a  warm 
place  for  some  hours.  It  is  insoluble  in  a  boiling  strong  solution  of 
ammonium  sulphate  rendered  alkaline  by  ammonium  hydrate  (distinc- 
tion from  calcium  sulphate). 
\.  The  other  reactions  are  similar  to  those  of  calcium. 

($)  DRY  REACTION. 
(To  be  also  practised  on  Sr(NO3)2.) 

A  platinum  wire  moistened  with  hydrochloric  acid,  dipped  in  the  substance 
and  introduced  into  the  inner  blowpipe  or  Bunsen  flame,  colours  the  outer 
flame  crimson. 


III.   CALCIUM  (Ca). 

.(a)    WET  REACTION'S. 

(To  be  practised  on  a  solution  of  calcium  chloride — CaCI2.) 

I.  (NH4)2C03  in  presence  of  NH4C1  and  NH4HO  (group  reagent)  produces  a 
white  precipitate  of  calcium  carbonate — CaCO3 — soluble  in  acetic  acid 
and  settling  best  on  warming. 

a.  (NH4)2C204  precipitates  white  calcium  oxalate — CaC2O4 — insoluble  in 
acetic  or  oxalic  acids,  but  soluble  in  hydrochloric  acid. 

3.  H2S04   in  strong  solutions  produces  a  precipitate  of  calcium  sulphate — 

CaSO4.  Being  slightly  soluble  in  water,  it  does  not  form  in  dilute 
solutions,  nor  is  it  precipitated  by  a  saturated  solution  of  calcium 
sulphate  (distinction  from  Ba  and  Sr).  It  is  soluble  in  a  boiling 
saturated  solution  of  ammonium  sulphate  containing  excess  of  ammo- 
nium hydrate,  but  quite  insoluble  in  a  mixture  of  two  parts  alcohol 
and  one  part  water. 

4.  Na2HP04  produces  a  white  precipitate  of  dicalcium  phosphate — CaHPO* 

— soluble  in  acetic  acid. 


(b)  DRY  REACTION. 
(To  be  practised  on  calcium  carbonate — CaCO3.) 

A  platinum  wire  moistened  with  hydrochloric  acid,  dipped  in  the  substance 
and  held  in  the  inner  blowpipe  or  Bunsen  flame,  colours  the  outer  flame 
yellowish-red.  This  reaction  is  masked  by  the  presence  of  barium  or 
strontium. 


26  DETECT  JON  OF  THE  MEIALS 


GROUP  V. 

Metals  not  precipitable  either  as  sulphide,  hydrate,  or  carbonate,  including 
magnesium,  the  precipitation  of  which  as  hydrate  or  carbonate  has  been 
prevented  by  the  presence  of  ammonium  chloride. 

I.  MAGNESIUM  (Mg). 

(a)    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  magnesium  sulphate — MgSO4.) 

1.  Na2HP04  in  the  presence  ofNHf.1  tf«^NH4HO  produces  a  white  crystalline 

precipitate  of  ammonium  magnesium  phosphate — MgNH4PO4.  It 
is  slightly  soluble  in  water,  and  scarcely  at  all  in  water  containing 
ammonium  hydrate,  but  entirely  soluble  in  all  acids.  In  very  dilute 
solutions  it  only  forms  on  cooling  and  shaking  violently,  or  on  rubbing 
the  inside  of  the  tube  with  a  glass  rod. 

2.  (NH4)2HAs04  produces  a  similar   precipitate   of  ammonium   magnesium 

arseniate — MgNH4AsO4 — possessing  like  features. 

3.  KHO,    NaHO,    and   NH4HO    give  precipitates  of  magnesium   hydrate— 

Mg(HO)2 — insoluble  in  excess,  but  soluble  in  the  presence  of 
ammonium  salts.  The  alkaline  carbonates  (except  ammonium  car- 
bonate) precipitate  magnesium  carbonate,  also  soluble  in  ammonium 
salts. 

4.  Calcium  hydrate  (lime  water)— C&(H.Q)2— and  Barium  hydrate  (baryta  water} 

— Ba(HO)2 — produce  a  similar  effect.  Either  of  these  reagents  is  useful 
for  the  separation  of  magnesium  from  all  the  alkalies  except  ammonium. 
The  solution,  which  must  contain  no  ammonium  salts,  is  treated  with 
excess  of  either  lime  or  baryta  water.  The  precipitated  magnesium 
hydrate  is  then  filtered  out  and  excess  of  ammonium  carbonate  added, 
which  precipitates  in  turn  the  excess  of  Ca  or  Ba  employed,  and  leaves 
K,  Na,  or  Li  in  solution. 

(l>)  DRY  REACTION. 
(To  be  practised  on  magnesium  oxide.) 

Heated  on  charcoal  before  the  blowpipe,  it  becomes  strongly  incandescent, 
and  leaves  a  white  residue,  which  when  moistened  with  a  drop  of  solution  of 
cobaltous  nitrate — Co(NOs)2 — and  again  heated,  becomes  rose-coloured. 
This  test  is  not,  however,  infallible. 

II.  LITHIUM  (Li). 
(a)    WET  REACTIONS. 

(To  be  practised  on  a  solution  of  lithium  chloride,  prepared  by  dissolving 
lithium  carbonate  in  dilute  hydrochloric  acid.) 

1.  Na2HP04  in  strong  solutions  produces  a  white  precipitate  of  lithium  phos- 

phate—(Li3PO4)^H2O— on  boiling  only  (distinction  from  Mg).  It  is 
soluble  in  hydrochloric  acid,  and  reprecipitated  by  boiling  with 
ammonium  hydrate. 

2.  Na2C03  and  even  NaHO,  in  very  strong  solutions,  yield  the  carbonate  and 

hydrate  respectively. 

3.  Platinic  chloride — PtCl4 — gives  no  precipitate  (distinction  from  potassium). 


POT  A  SSIUM— SODIUM— A  MMONIUM. 


b  DRY  REACTION. 
(To  be  practised  with  lithium  carbonate.) 

A  platinum  wire,  moistened  with  hydrochloric  acid,  dipped  in  the  substance 
and  held  in  the  inner  blowpipe  or  Bunsen  flame,  colours  the  outer  flame 
carmine  red.  The  presence  of  sodium  disguises  this  reaction. 

III.    POTASSIUM    (K). 
WET  REACTIONS. 

(To  be  practised  on  solution  of  potassium  carbonate  treated  with  dilute  HC1 
till  effervescence  ceases,  forming  potassium  chloride — KC1.) 

1.  PtCl4,  in  strong  solutions,  gives  a  yellow  crystalline  precipitate  of  potassium 

platino-chloride — PtCI4(KCl)2 — soluble  on  great  dilution,  especially  on 
warming,  but  insoluble  in  acids,  alcohol,  and  ether. 

2.  Hydrogen  tartrate  (tar tar ic  tf<^)— H2C4H406— throws  down,  from  strong 

solutions  only,  a  white  crystalline  precipitate  of  potassium  hydrogen 
tartrate — KHC4H4O6 — soluble  in  much  cold  water,  rather  freely  in 
hot  water,  readily  in  acids  and  in  KHO  or  NaHO,  and  not  formed 
unless  the  original  solution  be  nearly  neutral.  Its  separation  is  facili- 
tated by  stirring  and  shaking  violently,  in  which  case  it  settles  quickly. 

3.  Hydrogen  silicofluoride  (hydrofluosilidc  acid) — H2SiF6 — yields  white  gela- 

tinous potassium  fluosilicate — K2SiF6 — sparingly  soluble  in  water. 

DRY  REACTION. 
(To  be  practised  on  potassium  carbonate — K2CO3.) 

Dip  a  platinum  wire,  moistened  with  HCl,  in  the  salt.  Held  in  a  Bunsen 
flame  a  violet  colour  is  imparted.  The  masking  effect  of  Na  (yellow)  is  obviated 
by  viewing  the  flame  through  cobalt  glass. 

IV.  SODIUM  (Na). 

WET  REACTIONS. 

(To  be  tested  with  solution  of  sodium  chloride — NaCl.) 

1.  K2H.,Sb^07  (potassium  pyroantimoniate,   generally   called    metantimomate) 

— gives  a  white  granular  precipitate  of  sodium  pyroantimoniate — 
Na2H2Sb2O76H2O— from  strong  solutions  only,  which  must  be  neutral 
or  alkaline.  This  precipitate  is  insoluble  in  alcohol. 

2.  H2SiF6  gives  a  similar  precipitate  to  that  obtained  with  K  salts  in  concen- 

trated solutions  only. 

Sodium  salts  are,  practically,  all  soluble  in  water,  and  there  is  no  thoroughly 
trustworthy  wet  reaction  which  can  be  applied  to  detect  small  quantities.  If 
we  have  a  solution  which  gives  no  precipitate  with  any  of  the  group  reagenrs, 
but  leaves,  on  evaporating,  a  non-volatile  residue,  capable  of  imparting  a 
strong  yellow  colour  to  the  Bunsen  flame  (dry  reaction)  we  may  infer  with 
certainty  the  presence  of  sodium. 

V.    AMMONIUM    (NH4). 
WET  REACTIONS. 

(To  be  tested  with  solution  of  ammonium  chloride— NH4C1.) 
i.  PtCl4  produces  a  heavy  yellow  precipitate  of  ammonium  platino-chloride— 
PtCl4(NH4Cl)2— which,  being  rather  soluble  in  water,  is  not  formed  in 


28  DETECTION  OF  THE  METALS 

dilute  solutions,  unless  alcohol,  in  which  it  is  insoluble,  be  added  in 
considerable  quantity.  When  ignited,  pure  spongy  platinum  is  left 
This  precipitate  may  be  distinguished  from  that  with  K  salts  by  adding, 
after  ignition,  a  little  water  and  AgNO3,  when  no  white  precipitate  of 
AgCl  is  formed  (the  K  salt  leaves  KC1  on  being  strongly  heated). 

2.  H2C4H406  yields  ammonium  hydrogen  tartrate — (NH4)HC4H4O6 — almost 

identical  with  KHC4H4O6in  its  properties.  On  ignition,  however,  the 
latter  gives  a  black  residue,  which  turns  moistened  red  litmus  paper 
blue  (KoCOs  and  C),  the  former  leaving  pure  C  without  reaction. 

3.  NaHO  or  Ca(HO)2  boiled  with  the  solution  causes  the  evolution  of  ammonia 

gas — NH3.  A  glass  rod  dipped  in  HC1  or  HC2H3O2  produces,  when 
held  over  a  mixture  evolving  NH3,  white  clouds  (solid  NH4  salts),  and 
moist  red  litmus  paper  is  turned  blue. 

4.  Nessler's  Solution  (HgI2  dissolved  in  KI  and  KHO  added)  gives  a  yellow 

or  brown  colour,  or  a  brown  precipitate,  of  dimercuric  ammonium  iodide 
— NHg2IH2O — with  all  NH4  salts.  This  reaction  is  extremely  delicate, 
and  the  estimation  of  NH4  in  water  is  founded  upon  it. 

DR  Y  RE  A  CTIONS. 

Ammonium  salts  volatilise  (i)  with  decomposition,  leaving  a  fixed  acid 
{e-g-1  phosphate) ;  (2)  with  decomposition,  leaving  no  residue  whatever  (e.g., 
sulphate,  nitrate) ;  (3)  without  decomposition,  when  they  are  said  to  sublime 
(t.g;  chloride,  bromide,  etc.). 


CHAPTER    III. 
DETECTION  AND  SEPARATION  OF  ACID  RADICALS. 


I.   HYDROFLUORIC  ACID  and  FLUORIDES, 

(The  test  for  fluorides  undernoted  may  be  practised  on  fluor  spar — CaFj.) 

Hydrofluoric  Acid,  or  Fluoric  Acid,  is  known — 

1.  By  its  strongly  acid  reaction  and  corrosive  power. 

a.  By  its  action  upon  glass,  from  which  it  dissolves  out  silicic  acid  — 
SiO2 — thus  roughening  the  surface  and  rendering  it  semi-opaque 
or  translucent,  and  white ;  a  colourless  gas,  silicic  fluoride — 
SiF4 — passing  off. 

Fluorides  are  detected  as  follows : — 

The  mineral  or  salt  is  finely  powdered,  and  introduced  into  a  leaden  dish 
with  a  little  sulphuric  acid.  A  piece  of  glass,  previously  prepared  by  coating 
its  surface  with  wax,  and  etching  a  few  letters  on  the  waxed  side  with  the 
point  of  a  pin,  is  placed  over  the  dish,  waxed  side  down.  A  gentle  heat  is 
then  applied,  but  not  sufficient  to  melt  the  wax,  and  the  operation  continued 
for  some  time.  The  glass  is  then  taken  off,  and  the  wax  removed  from  it ; 
when,  if  fluorine  were  present,  the  letters  written  on  the  waxed  surface  will  be 
found  engraved  upon  it  by  the  action  of  the  hydrofluoric  acid. 

2.  CHLORINE,  HYDROCHLORIC  ACID,  and  CHLORIDES. 

'Free  Chlorine— C12— may  be  detected— 

1.  By  its  odour. 

2.  By  turning  paper  dipped  in  solution  of  potassium  iodide  brown. 

3.  By  bleaching  a  solution  of  indigo  or  litmus. 

Hydrochloric  Acid — HC1 — may  be  recognised — 

1.  By  its  acidity  and  its  giving  off  C12  when  heated  with  MnCX. 

2.  By  producing  dense  white  fumes  when  a  rod  dipped  in  ammonium 

hydrate  is  held  over  the  mouth  of  the  bottle. 

3.  By  giving  a  curdy  white  precipitate  of  argentic  chloride  with  argentic 

nitrate,  instantly  soluble  in  ammonium  hydrate. 

Chlorides  give  the  following  reactions    (to   be   practised   with   any   soluble 
chloride,  say  NaCl) : — 

1.  Heated  with  sulphuric  acid  they  evolve  white  fumes  of  HC1. 

2.  Heated  with  H_,S04  and  MnO,  they  evolve  chlorine. 

3.  AgN03  in  the  presence  0/HN03  gives  a  white  precipitate  of  argentic 

chloride— AgCl— insoluble  in  boiling  nitric  acid,  but  instantly 
soluble  in  dilute  ammonium  hydrate  of  a  strength  of  i  in  20. 


30  DETECTION,   ETC.,    OF  ACID  RADICALS. 

4.  The  solid  substance  mixed  with  K2Cr.,07,  and  distilled  with  H2S04, 
yields  chloro-chromic  oxide-  CiCl2O2 — in  red  fumes  which, 
when  passed  into  dilute  ammonium  hydrate,  colour  it  yellow, 
owing  to  the  formation  of  ammonium  chromate — (NH4)2CrO4. 
The  yellow  should  change  readily  to  green  on  the  addition  of  a 
few  drops  of  sulphurous  acid. 

Insoluble  Chlorides  should  be  first  boiled  with  strong  sodium  hydrate  and 
the  whole  diluted  and  filtered.  The  chloride  is  then  transferred  to  the 
sodium,  and  is  to  be  searched  for  in  the  filtrate  by  acidulating  with  nitric  acid 
and  adding  argentic  nitrate,  as  above  described. 

3.  HYPOCHLORITES. 

(Practise  on  a  solution  of  chlorinated  lime — Ca(ClO)2CaCl2.) 

Hypochlorites  are  all  readily  soluble  in  water,  are  contained  in  the  so-called 
chlorinated  compounds,  and  are  recognised — 

1.  By  having  an  odour  of  chlorine. 

2.  By  giving  a  blue  with  potassium  iodide,  starch  paste,  and  acetic 

acid,  due  to  liberation  of  chlorine. 

4.  CHLORATES. 

(To  be  practised  on  potassium  chlorate — KC1O3.) 

1.  Heated  on  charcoal,  they  deflagrate. 

2.  Heated  with  strong  sulphuric  acid,  they  evolve  chlorine  peroxide — 

ClaO4 — which  is  yellow  and  explosive. 

3.  Their  solutions  yield  no  precipitate  with  argentic  nitrate  ;  but  if  a 

little  of  the  solid  be  heated  to  redness,  and  the  residue  dissolved 
in  water,  a  precipitate  of  argentic  chloride  may  be  obtained. 
The  same  reduction  from  chlorate  to  chloride  may  also  be 
effected  by  adding  zinc  and  dilute  sulphuric  acid  to  the  solution. 

4.  Mixed  with  KI  and  starch  paste,  and  acidulated  with  acetic  acid, 

they  give  no  blue  (distinction  from  hypochlorites),  but  on 
adding  HC1  a  blue  is  developed. 

5.  PERCHLORATES. 

These  are  distinguished  from  chlorates — 

1.  By  giving  off  perchloric  acid  — HC1O4 — when  heated  with  sulphuric  acid,  without 

explosion  or  evolution  of  chlorine  peroxide. 

2.  Like  chlorates,  they  require  reduction  to  chlorides  before  giving  a  precipitate  with 

argentic  nitrate. 

6.  BROMINE,  HYDROBROMIC  ACID,  and  BROMIDES. 

Bromine — Br2—  is  distinguished — 

1.  By  its  appearance — heavy,  reddish-brown  liquid,  giving  off  reddish 

fumes  of  a  very  penetrating,  unpleasant  odour. 

2.  By  turning  starch  paste  orange. 

3.  When  present  in  small  quantity  in  solution,  on  adding  a  few  drops 

of  chloroform  and  shaking,  an  orange  colour  is  imparted   to 
that  liquid,  which  sinks  to  the  bottom  of  the  aqueous  solution. 
Hydrobromic  Acid— HBr — is  known — 

By  its  acid  reaction  and  the  production  of  fumes  of  bromine  when 
heated  with  strong  sulphuric  acid. 


BROMIDES— IODIDES.  31 

Bromides  are  all  soluble  in  water,  except  the  silver,  mercurous,  and  lead  salts  ; 
they  are  detected  by  the  following  characters  (to  be  practised 
on  potassium  bromide— KBr)  : — 

1.  Heated  with  strong   sulphuric  acid,  they  evolve  red  vapours  of 

bromine. 

2.  A  similar  effect  is  produced  by  sulphuric  acid  and  metallic  dioxides, 

such  as  PbO2,  MnO2. 

3.  Mixed  with  starch  paste,  and  a  few  drops  of  chlorine  water  care- 

fully added,  they  give  an  orange  colour  (starch  bromide). 

4.  Mixed  in  a  long  tube  with  chloroform,  and  a  few  drops  of  chlorine 

water  added,  the  whole,  when  shaken  well  together,  leaves,  on 
settling,  a  characteristic  reddish-brown  stratum  at  the  bottom  of 
the  liquid  in  the  tube,  due  to  free  bromine  in  the  chloroform. 

5.  With  argentic  nitrate  they  give  a  dirty-white  precipitate  of  argentic 

bromide,  insoluble  in  nitric  acid,  slowly  soluble  in  ammonium 
hydrate,  but  insoluble  in  dilute  NH4HO,  of  a  strength  of  i  in 
20  (argentic  chloride  dissolves). 

6.  Distilled  with  potassium  dichromate  and  sulphuric  acid,  red  fumes 

are  evolved,  which  give  no  colour  when  passed  into  ammonium 
hydrate  (distinction  from  chlorides). 

Insoluble  Bromides  should  be  first  boiled  with  NaHO,  as  described  under 
insoluble  chlorides. 

7.  HYPOBROMITES. 

These  are  very  similar  to  hypochlorites,  and  react  as  follows: — 

1.  They  decompose  by  heat,  leaving  a  bromide  ; 

2.  On  boiling  with  an  alkali,  a  mixture  of  bromide  and  bromate  results. 

8.  BROMATES. 

These  are  recognised  — 

1.  By  deflagrating  on  charcoal,  leaving  the  corresponding  bromide. 

2.  By  liberating  bromine  on  the  addition  of  dilute  sulphurous  acid. 

9.  IODINE,  HYDRIODIC  ACID,  and  IODIDES. 

Iodine — 12 — may  be  recognised  by  its  glistening  black  scales,  its  odour,  the 
violet  vapour  on  heating,  and  the  production  of  blue  iodide  of  starch  on 
adding  a  solution  to  starch  paste. 

Hydriodic  Acid— HI — in  the  gaseous  state,  is  detected  by  the  formation  of 
a  brown  colour  on  paper  moistened  with  chlorine  water  (blue  if  also  dipped 
in  starch  paste)  held  over  a  tube  from  which  it  is  being  evolved. 

Iodides  are  readily  known  by  the  following  reactions  (which  may  be 
practised  on  a  solution  of  potassium  iodide,  KI) : — 

1.  Heated  with  strong  sulphuric  acid  they  give  a  liberation  of  iodine 

with  violet  fumes. 

2.  Mucilage  of  starch  and  chlorine  water  or  strong  nitric  acid  (if  not 

added  too  plentifully)  produces  blue  iodide  of  starch,  decom- 
posed by  heat,  but  re-formed  on  cooling ;  also  bleached  by 
excess  of  Cl. 

3.  AgN03  gives  a  light  yellow  precipitate  of  argentic  iodide — Agl. 

The  precipitate,  when  freed  from  the  supernatant  liquid,  does 
not  dissolve  in  hot  HNO3,  and  is  practically  insoluble  in 
ammonium  hydrate,  being  thus  distinguished  from  a  chloride 


32  DETECTION,   ETC.,    OF  ACID  RADICALS. 

4.  A  neutral  solution  gives  with  one  part  of  cupric  sulphate — CuSO4 

—and  three  parts  of  ferrous  sulphate— FeSO4— dissolved  in 
a  little  water,  a  greyish  precipitate  of  cuprous  iodide — Cu.2I2. 

The  same  precipitate  is  produced  if  sulphurous  acid— H^SOa 
— be  used  with  the  cupric  sulphate  instead  of  ferrous  sulphate. 

5.  Palladious  Chloride— PdCl,— or  palladious  nitrate— Pd(N03)2— 

gives  a  black  precipitate  of  palladious  iodide — PdI2 — decom- 
posed somewhat  below  the  temperature  of  boiling  mercury, 
iodine  being  evolved,  and  the  metal  left.  This  is  a  very 
expensive  but  efficient  separation. 

6.  Mercuric  chloride  and  plumbic  nitrate  give  respectively  red  and 

yellow  precipitates  with  soluble  iodides. 


10,   IODATES. 

(Practise  on  solution  of  potassium  iodate — KIO3.) 

lodates  are  known — 

1.  By  giving,  when  heated  with  strong  sulphuric  acid,  similar  reactions  to  those 

obtained  with  chlorates. 

2.  By  giving  a  blue  colour  with  starch  paste  on  the  addition  of  sulphurous  acid. 

3.  By  giving  a  blue  colour  with  starch  paste  on  the  addition  of  potassium  iodide 

and  tartaric  acid. 

4.  By  yielding  a  precipitate  of  ferric  oxy-iodate  on  adding  ferric  chloride. 

11.   PERIODATES. 

Periodates  are  distinguished— 

I.  By  giving  a  precipitate  with  BaCL,  in  a  neutral  solution,  which  is  not  decomposed 
by  digesting  with  ammonium  carbonate  and  a  little  NH4HO.     lodates  leave 
barium  carbonate,  which  when  washed  dissolves  in  acid  with  effervescence. 
I.   By  adding  Hg(NO3)2  and  treating  the  yellowish  precipitate  with  SnCl,.     It  turns 

green,  HgI2  being  produced. 
• 

12.   WATER  and  HYDRATES. 

Water  is  recognised — 

1.  By  its  absolute  neutrality  to  test-paper. 

2.  By  its  evaporating  without  residue,  fumes,  or  odour  of  any  kind. 

3.  By  its  turning  white  anhydrous  cupric  sulphate  blue. 

4.  By  yielding  pure  hydrogen  when  it  is  boiled  and  the  steam  passed 

slowly  over  copper  turnings  heated  to  bright  redness  in  an  iron 
tube. 

5.  By  its  undergoing  electrolysis  when  acidified,  yielding  hydrogen  at 

the  negative  and  oxygen  at  the  positive  electrode. 

The  soluble  Hydrates,  viz.,  KHO,  NaHO,  LiHO,  Ba(HO)2,  Sr(HO)2,  and 
Ca(HO).2  are  known— 

1.  By   being  more  or   less   soluble  in   cold  water,  yielding  solutions 

which  are  strongly  alkaline  to  test-paper. 

2.  By  dissolving  in  hydrochloric  acid  without  effervescence  and  without 

smell. 

3.  By  giving  a  brownish-black  precipitate  of  argentic  oxide — Ag2O — 

with  argentic  nitrate. 

The  insoluble  Hydrates  are  recognised — 

By  giving  off  steam  when  heated  in  a  dry  test-tube,  and  leaving  a 
residue  which  behaves  like  the  corresponding  oxide. 


OXIDES-SULPHIDES.  33 

13.   OXIDES. 

All  oxides  are  insoluble  in  water.      Oxides  of  K,  Na,  Li,  Ba,  Sr,  and  Ca 
unite  with  water  to  form  hydroxides,  which  dissolve  with  a  greater  or  less 
degree  of  readiness  and  give  the  characters  of  the  soluble  hydrates  already 
mentioned. 
Normal  Oxides  can  only  be  recognised  by  negative  results,  such  as  : — 

1.  Heated  alone,  they  are  not  changed;  except  argentic  oxide,  which 

leaves  the  metal,  and  mercuric  oxide,  which  volatilises  and 
breaks  up  into  the  metal  and  oxygen. 

2.  They  are  insoluble  in  water  (exceptions  K,  Na,  etc.,  as  above),  hut 

soluble  in  hydrochloric  or  nitric  acid  without  effervescence  and 
without  smell. 

3.  After  dissolving  and  removing  the  metal  by  H2S   or  Na2(J03  as 

most  convenient,  no  acid  radical  is  found,  other  than  that  of 
the  acid  used  to  dissolve. 

4.  Boiled  with  strong  NaHO  and  filtered,  or  fused  with  KNaC03  and 

digested  with  water,  the  solution  gives  no  reaction  for  any  acid 
radical  except  the  soluble  hydrate  or  carbonate  employed. 
Peroxides,  on  account  of  their  containing  an  excess  of  oxygen,  differ  from 
normal  oxides  (practise  on  MnO2), — 

1.  By  giving  off  oxygen  when  strongly  heated. 

2.  By  evolving  chlorine  when  heated  with  hydrochloric  acid. 

14.   SULPHITE,  HYDROSULPHURIC  ACID,  and  SULPHIDES. 

Ordinary  Sulphur — S2  or  S6 — is  recognised — 

1.  By  its  burning  entirely  away  with  a  pale  blue  flame,  and  evolving 

sulphurous  anhydride. 

2.  By  its  insolubility  in  all  ordinary  menstrua,  such  as  water,  alcohol, 

and  ether,  but  dissolving  readily  in  carbon  disulphide. 

3.  When  slowly  heated  in  a  tube,  it  first  melts,  then  thickens,  then 

liquefies  again,  and  finally  boils,  the  vapour  taking  fire  and 
forming  sulphurous  anhydride. 

Precipitated  Sulphur  possesses  the  above  characters,  and  is  specially  distin- 
guished from  ordinary  sulphur  by  being  quite  amorphous  under 
the  microscope,  while  the  latter  is  crystalline. 

Hydrosulphuric  Acid — H2S  (sulphuretted  hydrogen) — is  known — 

1.  By  being  a  colourless  gas  with  a  disgusting  odour  of  rotten  eggs. 

It  is  inflammable,  burning  in  the  air  to  produce  sulphurous 
acid. 

2.  By  turning  a  piece  of  paper  black,  which  has  been  moistened  with 

solution  of  plumbic  acetate  and  held  over  the  mouth  of  the 
tube  or  jet  from  which  it  issues. 
Normal  Sulphides  are  divisible  into  five  classes  :— 

1.  Soluble  in  water,  including  the  sulphides  of  K,  Na,  NH4,  Ca,  sr, 

Ba,  and  Mg. 

2.  Insoluble  in  water,  but  readily  soluble  in  dilute  hydrochloric  acid 

including  those  of  Fe,  Mn,  Zn. 

3.  Insoluble  in  dilute,  but  soluble  in  strong  boiling  hydrochloric  acid, 

including  the  sulphides  of  Ni,  Co,  Sb,  and  Sn  (PbS  is  also 
slightly  affected,  but  separates  on  cooling,  as  chloride). 

4.  Insoluble  in  hydrochloric  acid,  but  attacked  by  strong  heated  nitric 

acid,  being  converted  wholly  or  partially  into  su'phates.  These 
include  the  sulphides  of  Pb,  Ag,  Bi,  Cu  (arsenious  sulphide  is 
slowly  affected). 


34  DETECTION,   ETC.,    OF  ACID  RADICALS. 

5.  Not  dissolved  by  any  single  acid,  but  converted  into  a  soluble 
sulphate  by  the  action  of  nitre-hydrochloric  acid,  or  hydro- 
chloric acid  and  potassium  chlorate;  including  those  of 
Hg,  As,  Au,  and  Pt. 

Sulphides  soluble  in  water  or  in  hydrochloric  acid  are  recognised  (practise 
on  soluiion  of  NagS) — 

1.  By  giving  off  sulphuretted  hydrogen  when  heated  with  HC1. 

2.  Soluble  sulphides  give  black  and  yellow  precipitates,  with  solutions 

of  lead  and  cadmium  respectively. 

3.  Alkaline  sulphides  give  a  purple  colour  with  sodium  nitroprusside 

-Na,Fe(NO)C6N6. 

Sulphides  insoluble  in  hydrochloric   acid  are   best   detected   (practise   on 
vermilion) — 

1.  Mix  a  little  with  sodium  carbonate  and  borax,  and  heat  on  charcoal 

before  the  blowpipe.  Remove  the  mass  thus  obtained,  place 
it  on  a  clean  silver  coin,  and  moisten  with  a  drop  of  distilled 
water  ;  when,  owing  to  the  formation  during  ignition  of  sodium 
sulphide — Na_S,— a  black  stain  of  argentic  sulphide — Ag^S — 
will  be  produced. 

2.  By  heating  with  strong  nitric  or  nitro-hydrochloric  acid,  diluting 

the  solution,  and  testing  for  a  sulphate  with  barium  chloride 
(see  page  36). 

3.  By  fusion  with  KNaC03  and  KNOs,  digesting  the  residue  in  water, 

filtering  and  testing  the  solution  for  a  sulphate* — formed  by  the 
oxidising  action  of  the  potassium  nitrate. 

Polysulphides  as  commonly  met   with  are  those  of  the  alkalies,  and   are 
soluble  in  water.  They  are  known  (practise  on  sulphuretted  potash — K2Ss) — 

1.  By  the  deep  yellow  or  orange  colour  of  their  solutions. 

2.  By  evolving  sulphuretted   hydrogen   accompanied  by   a   deposit  oj 

sulphur  when  treated  with  hydrochloric  or  dilute  sulphuric 
acids. 

The  polysulphides  which  are  insoluble  in  hydrochloric  acid,  such  as  iron 
pyrites,  copper  pyrites,  etc.,  are  best  proved  by  fusion  with  potassium  nitrate 
and  carbonate  and  conversion  into  sulphate.  They  may,  however,  be  recog- 
nised by  heating  with  hydrochloric  acid  and  zinc,  when  the  excess  of  sulphur 
will  pass  off  as  H2S,  leaving  the  normal  sulphide. 

15    THIOSULPHATES   (Hyposulphites). 
(Practise  on  solution  of  sodium  thiosulphate — Na^S-XXjS  H2O.) 

These  salts,  commonly  known  as  hyposulphites,  are  usually  soluble  in  water, 
and  exhibit  the  following  characters  : — 

i.  With  either  dilute  or  strong  HC1  and  H.,S04,  they  give  off  SO, 
and  form  a  yellow  deposit  of  S  (distinction  from  sulphides, 
polysulphi.tes,  and  sulphites], 

i.  AgNO^  gives  no  precipitate  at  first,  owing  to  excess  of  a  hypo- 
sulphite dissolving  argentic  hyposulphite — Ag.,S2O3 — but  on 
continuing  the  addition,  this  Ag2S2Os  is  precipitated  of  a  white 
colour.  The  salt  splits  up  spontaneously,  becoming  yellow, 
brown,  and  lastly  black,  and  being  changed  completely  into 
argentic  sulphide— Ag2S.  The  same  decomposition  of  the 
precipitate  occurs  on  substituting  HgNO^  or  Pb(NO3).2  for 
AgNO,;  and  in  all  three  cases  heat  accelerates  the  action, 
and  HJ5O4  is  the  by-product. 


SULPHITES  AND  SULPHATES.  35 

3.  Fe.,Cl6  produces  a  reddish-violet  colour,  gradually  disappearing  as 

FeCL,  is  formed.  (This  colour  is  not  produced  by  sulphites^  and 
a  somewhat  similar  tint  produced  by  Fe2Cl6  in  thiocyanatss  does 
not  disappear.} 

4.  Na.,OCl2  or  C12  water  converts  hyposulphites  into  sulphates,  even 

without  applying  heat. 

16.   SULPHUROUS  ACID  and  SULPHITES. 

Sulphurous  Acid — H2S03 — is  recognised  in  solution— 

1.  By  its  pungent  odour  of  burning  sulphur,  due  to  evolution  of  SO^. 

It  combines  directly  with  peroxides  to  form  sulphates.  Foi 
instance  : — 

PbO,  +  SO2  =  PbSO4. 

(This  reaction  is  utilised  in  gas  analysis,  to  separate  SO2  from  a 
mixture.) 

2.  By  adding  barium  chloride  in  excess,  filtering  out  any  precipitate 

of  barium  sulphate  which  may  form  (owing  to  the  fact  that 
all  samples  of  the  ordinary  acid  contain  sulphuric  acid),  and 
then  adding  chlorine  water  and  getting  another  copious  white 
precipitate  of  barium  sulphate,  owing  to  the  conversion  of  the 
sulphurous  into  sulphuric  acid  by  the  oxidising  action  of  the 
chlorine  water,  thus  :  — 
H2S03  +  BaCl2  +  Cl,  +  H2p  =  BaSO4  +  4HC1. 

3.  Treated  with  zinc  and  hydrochloric  acid,  it  evolves  sulphuretted- 

hydrogen,  thus  : — 

3Zn  +  6HC1  +  H,S03  =  3ZnCl?  +  H2S  +  3H2a 

4.  When  a  solution  of  iodine  is  dropped  into  the  liquid,  its  colour  is- 

discharged,  owing  to  its  conversion  into  hydriodic  acid  by  the 
hydrogen  of  the  water,  the  oxygen  of  which  passes  at  the  same 
time  to  the  sulphurous  acid,  forming  sulphuric  acid. 
H.S03  +  I2  +  H20  =  H2S04  +  2HI. 

Sulphites  are  known  by  the  following  characteristics  (practise  on  solution  of 
sodium  sulphite — Na2SO3) : — 

1 .  All  except  the  alkaline  sulphites  are  sparingly  soluble  in  water. 

2.  When  heated  with  sulphuric  acid  they  evolve  sulphurous  anhydride,. 

witnbut  deposit  of  sulphur. 

3.  Acted  on  with  zinc  and  hydrochloric  acid,  they  evolve  sulphuretted 

hydrogen,  which  blackens  a  piece  of  paper  moistened  with. 
plumbic  acetate  and  held  over  the  mouth  of  the  test-tube. 

4.  A  salt  of  silver,  mercury,  or  lead   produces  a  precipitate  which  on. 

heating  turns  dark,  owing  to  the  formation  of  a  sulphide  and 
free  sulphuric  acid. 

5.  By  boiling  with  barium  chloride  and  chlorine  water  or  nitric  acid, 

barium  sulphate  is  produced,  and  precipitates. 

6.  K2Cr.,07  and  HC1  give  a  green  coloration   of  chromic  sulphate  01 

chloride.  This  test  is  very  delicate,  but  by  itself  is  not  con- 
clusive, as  any  reducing  agent  acts  similarly. 

17.   SULPHURIC  ACID  and  SULPHATES. 

Sulphuric  Acid—  H,S04 — is  detected— 

1.  By  its  appearance.     A  heavy,  oily,  odourless,  and  nearly  colourless 

liquid,  powerfully  acid  and  corrosive. 

2.  By  its  charring  effect.     This  is  made  evident  when  the  strong  acid 

is  dropped  upon  white  paper,  wood,  etc.,  or  when  the  dilute 


30  DETECTION,.  El C.,    OF  ACID  RADICALS. 

acid  is  evaporated  in  a  basin  containing  a  little  white  sugar. 
The  carbonisation  is  due  to  the  power  the  acid  has  of  abstract- 
ing the  elements  of  water  from  organic  bodies. 

3.  By  liberating  an  explosive  gas  when  dropped  on  a  small  fragment  of 
KC103. 

Sulphates  are  soluble  in  water,  with  the  exception  of  basic  sulphates  (soluble 
in  acids)  and  BaSO^,  SrSO4)  CaSO4,  and  PbSO4.  (Ag2S04  is  only  slightly 
soluble.)  When  it  is  necessary  to  analyse  such  sulphates  as  are  insoluble 
in  dilute  acids,  they  are  decomposed,  either  by  boiling  with  potassium 
or  sodium  hydrates  or  by  fusion  with  KNaCOg  (the  latter  being  preferable), 
and  extracting  the  fused  mass  with  water  when  the  sulphate  passes  into  solu- 
tion. Sulphates  are  recognised  by  the  following  characters  (practise  on  solution 
of  magnesium  sulphate)  :— 

1.  BaCl2  or  Ba(NOa)2  produces  a  white  precipitate  of  barium  sulphate 

— BaSO4 — insoluble  in  boiling  water  and  boiling  nitric  acid. 
The  addition  of  barium  chloride  to  a  strongly  acid  solution 
often  causes  the  reagent  to  crystallise  out,  and  this  is  then 
mistaken  by  the  student  for  a  true  precipitate  of  sulphate ; 
therefore  the  boiling  water  should  always  be  employed. 

2.  The  addition  of  a  soluble  salt  of  lead  or  strontium  also  causes  the 

formation  of  insoluble  sulphates ;  but  these  reactions  are  never 
used  in  practice,  the  barium  chloride  being  at  once  the  most 
delicate  and  serviceable  reagent. 

3  Heated  with  a  little  Na2C03  on  charcoal  in  the  inner  blowpipe 
flame,  sulphates  are  reduced  to  sulphides;  and  the  residue, 
placed  on  a  clean  silver  coin  and  moistened  with  water,  leaves 
a  black  stain. 

18.   CARBON,  CARBONIC  ACID,  and  CARBONATES. 

Carbon — C2 — is  known — 

1.  By  its  black  colour  and  by  burning  in  the  air  and  producing  a  gas 

which  is  odourless,  so  heavy  that  it  can  be  poured  from  one 
vessel  to  another,  and  causes  a  white  precipitate  when  passed 
into  solution  of  calcium  hydrate. 

2.  By  its  capability  of  removing  many  vegetable  colouring  matters 

from  their  solutions. 

Carbonic  Acid — H2C03 — is  not  known  in  the  free  state,  as  it  splits  up  into 
carbonic  anhydride — CO2 — and  water  on  isolation.     CO2  is  recognised — 

1.  By  being  odourless  and  giving  white  insoluble  CaCO^  (or  BaCO3) 

when  passed  into  a  solution  of  Ca(HO)2  (or  Ba(HO).,). 

2.  By  turning  blue  litmus  purple  or  wine-red,  the  original  tint  being 

restored  by  heat,  the  CO2  escaping. 

Carbonates  are  mostly  insoluble  in  water,  the  alkaline  carbonates  alone 
dissolving.  All  carbonates  give  off  CO2  on  ignition,  except  K.2CO3  and 
Na2CO3.  A  white  heat  is  needed  to  decompose  BaCO3  and  SrCO3.  Most 
carbonates  on  heating  to  redness  leave  the  oxide.  Their  recognition  depends 
upon  the  following  reactions  (practise  upon  calcium  carbonate) — 

1.  Effervescence  with  a  solution  of  almost  any  acid  (H2S  and  HCN 

excepted),  organic  or  inorganic,  and  giving  off  an  odourless 
gas— CO2. 

2.  When  the  gas  given   off  is  poured  or  passed   into  a  solution  of 

calcium  hydrate,  a  white  precipitate  of  CaCO3  falls,  soluble  in 
excess  of  CO2.  When  CO2  is  given  off  along  with  H2S  or  SOg, 


BORATES,    AND   SILICATES. 


either  of  these  may  be  removed  by  passing  through  K2CrO4 
and  HC1,  which  is  rendered  green,  and  the  unacted-upon  CO2 
is  allowed  to  pass  into  calcium  hydrate  solution  as  before,  thus 
enabling  us  to  detect  a  carbonate  in  the  presence  of  a  sulphide 
or  sulphite. 

3  HgCLj  gives  a  reddish-brown  precipitate  with  the  carbonates  of 
of  K,  Na,  and  Li,  and  a  white  one  with  bicarbonatcs  of  the  same 
metals. 

4.  Soluble  carbonates  give  a  white  precipitate  with  cold  solution  of 
MgSO4,  while  bicarbonates  do  not. 

19.   BORIC  ACID  and  BORATES. 

Boric  (or  Boracic)  Acid  —  H3BO?  —  is  distinguished  as  under  :  — 

1.  It  is  a  white  crystalline  solid,  giving  off  water  on  being  heated,  and 

leaving  the  anhydride  —  B2O3. 

2.  A  solution  in  alcohol  burns  with  a  green  flame. 

3.  When  dissolved  in  hot  water,  and  a  piece  of  turmeric  paper  dipped 

in  the  solution,  the  yellow  colour  is  unaffected  ;  but  upon  drying 
the  paper  it  becomes  brownish-red,  turned  green  on  moistening 
with  KHO. 

All  borates  dissolve  in  dilute  acids,  but  few  in  water,  and  when 
decomposed  by  hot  acids,  let  fall  crystalline  boric  acid  on> 
cooling,  which  answers  to  the  above  characters. 

The  presence  of  soluble  borates  is  detected  by  the  following  tests  (practise 
upon  borax  —  Na2B4O7ioH,O  :  — 

1.  They   give,  on   heating   with   calcium   chloride,  rendered  slightly 

alkaline  with  ammonium  hydrate,  a  white  precipitate  of  calcium 
borate,  soluble  in  acetic  acid,  and  so  distinguished  from  oxalate. 

2.  On  rendering  the  solution  just  acid  with  hydrochloric  acid,  it  reacts 

with  turmeric  paper  as  does  H3BO3. 

3.  Besides  these  two  tests,  which  are  in  themselves,  taken  together, 

quite  conclusive,  borates  give  a  white  precipitate  with  argentic 
nitrate  soluble  in  nitric  acid. 

4.  When   a   little   of  the  solid   borate  is  moistened  with  a  drop  of 

sulphuric  acid,  and  alcohol  is  added,  the  green  flame  of 
HoBO3  is  obtained  on  applying  a  light. 

20.   SILICIC  ACID  and  SILICATES. 

The  acid  H4Si04  is  scarcely  ever  met  with,  and  we  have  practically  to  deal 
with  the  anhydride  —  SiC>2  —  which  is  totally  insoluble  in  water  and  dilute"  acids, 
the  acid  dissolving  slightly  in  both.  SiO2  is  characterised  — 

1.  By  its  infusibility  when  heated. 

2.  By  its  insolubility  in  water,  and  all  acids  except  HF. 

3.  By  forming  when  heated  with  H2S04  and  CaF.,  in  a  leaden  vessel. 

gaseous  silicic  fluoride  —  SiF4  —  which  deposits  the  acid  —  H4SiO4 
—  and  forms  hydro-fluosilicic  acid  —  H£SiF6  —  in  contact  with 
moisture. 

Silicates  are  insoluble  in  water,  except  the  alkaline  silicates.  Many  of 
them  do  not  dissolve  in  strong  acids  (a  few  are  decomposed  by  hot  H2SO4, 
but  by  no  other  acid),  but  all  are  split  up  by  the  action  of  gaseous  hydrofluoric 
acid  or  a  mixture  of  CaF2  and  HLSO4. 

i.  On  adding  HC1  to  an  alkaline  silicate,  H4SiO4  falls  as  a  gelatinous 


$8  DETECTION,   ETC.,    OF  ACID  RADICALS. 

— scarcely  visible — precipitate,  slightly  soluble  in  water.  On 
evaporating  to  dryness  and  heating  to  140°  or  150°  C.,  the 
addition  to  the  residue  of  a  little  HC1  and  water  leaves  the  SiO8 
as  a  white  gritty  powder. 

2.  NH4C1  precipitates  H4SiO4  from  an  alkaline  silicate. 

3.  Silicic  anhydride  is  separated  from  all  acid  and  basic  radicals  by 

fusing  the  finely  powdered  silicate  with  KNaCO3  (fusion  mix- 
ture], in  a  platinum  crucible;  adding  dilute  HC1  to  the  residue 
till  effervescence  ceases,  evaporating,  and,  when  dry,  heating  to 
140°  or  150°  C.  On  again  treating  this  residue  with  water  and 
HC1,  SiO2  alone  remains  insoluble. 


21.   HYDROFLTJOSILICIC  ACID  (H2SiF6). 

This  acid  is  only  known  in  solution. 

I.  It  is  very  acid,  and  dissolves  metals  with  the  evolution  of  hydrogen,  forming 
silico  fluorides  which  decompose  by  heat,  leaving  fluorides,  and  giving  off 
silicon  fluoride—  SiF4. 
~*.  It  gives  off  hydrofluoric  acid  when  evaporated,  and  should  not,  therefore,  be 

heated  in  glass  vessels,  as  they  would  be  etched. 

.J.  The  majority  of  silico-fluorides  are  soluble,  the  exceptions  being  K3SiFg, 
BaSiF6,  and  Na2SiF6,  which  are  insoluble,  especially  in  presence  of  a  little 
alcohol. 

'4.  It  does  not  precipitate  strontium  salts,  even  from  strong  solutions,  but  throws 
down  BaSiF6  on  adding  BaCl2  and  alcohol,  as  a  white  translucent  crystalline 
precipitate. 
$.  Potassium  salts  throw  down  gelatinous  K2SiF6. 


22.   NITROUS  ACID  AND  NITRITES. 

'Nitrons  Acid   (so   called   commercially)   is   nitric   acid    containing    nitrous 
anhydride.     It  is  yellowish  in  colour,  and  evolves  reddish  fumes. 

~  Nitrites  are  all  soluble  in  water,  the  least  so  being  argentic  nitrite.     They  are 
known  as  follows  (practise  upon  potassium  nitrate  which  has  been  heated 
vto  dull  redness  or  upon  sodium  nitrite — NaNO2) : — 

j.  They  give  red  fumes  when  treated  with  strong  sulphuric  acid. 

2.  They  give  an  instantaneous  blue  colour  with  potassium  iodide  and 

starch  paste  on  the  addition  of  a  few  drops  of  dilute  sulphuric 
.acid.  The  sulphuric  acid  liberates  hydriodic  acid  from  the 
iodide,  and  nitrous  acid  from  the  nitrite ;  the  hydriodic  acid 
is  decomposed  by  the  nitrous  acid  into  iodine,  water,  and  nitric 
oxide  : — 

2HNO2  +  2HI  =  I,  +  2H,0  f  2NO. 

[Nitrates,  it  must  be  remembered,  would  give  frequently  a  similar  reaction  after 
starding,  through  the  possible  reduction  of  some  portion  of  their  nitric  acid 
to  nitrous  acid  ;  so  that  unless  the  reaction  appears  instantly,  and  is  confirmed 
by  others,  it  is  not  safe  to  rely  upon  it  as  a  test.] 

3.  -They  give  a  dark  brown  colour  with  ferrous  sulphate  without  the 

previous  addition  of  sulphuric  acid,  as  required  by  nitrates. 

4.  Potassium  dichromate  in  solution  is  converted  into  a  green  liquid 

by  the.  addition  of  a  nitrite  and  an  acid.  These  two  latter 
substances  also  reduce  solution  of  auric  chloride,  forming  a 
precipitate  of  the  metal,  possessing  a  dark  colour. 


NITRIC  ACID  AND  NITRATES.  39 


23.   NITRIC  ACID  and  NITRATES. 

Nitric  Acid — HN03 — is  strongly  acid  and  corrosive,  fumes  in  tne  air,  and 
readily  dissolves  most  metals.  It  may  be  at  once  recognised  by  the  following 
characters  : — 

1.  When  poured  on  a  piece  of  copper  foil,  and  a  piece  of  white  paper 

held  behind  the  test-tube,  orange-red  fumes  of  nitric  peroxide 
— NgO* — are  observed. 

2.  When  dropped  on  a  piece  of  quill  in  a  basin,  or  evaporated  in 

contact  therewith,  the  quill  is  stained  yellow,  intensified  to 
orange  on  adding  an  alkali,  and  not  discharged  by  warming 
(distinction  from  the  corresponding  stains  produced  by  iodine  and 
bromine). 

3.  Dropped   on   a  few  crystals   of   brucine,   a  deep  red  colour  is 

produced. 

Nitrates  are  characterised  by  the  following  properties  (practise  upon  solution 
of  potassium  nitrate — KNCK) : — 

1.  All  nitrates  are  soluble  in  water,  especially  when  slightly  acidulated 

with  nitric  acid.  The  nitrates  of  the  alkalies  are  only  decom- 
posed by  a  very  high  temperature,  but  nitrates  of  the  heavy 
metals,  such  as  copper,  mercury,  and  lead,  are  readily  decom- 
posed by  heat,  leaving  a  residue  of  oxide.  (Argentic  nitrate 
leaves  metallic  silver.) 

2.  When  heated  with  sulphuric  acid,  they  evolve  pungent  fumes  of 

nitric  acid. 

3.  When  heated  with  sulphuric  acid  and  a  piece  of  copper  wire,  red 

fumes  of  nitric  peroxide  are  formed  in  the  tube. 

4.  When  mixed  with  a  solution  of  ferrous  sulphate  in  the  presence  of 

sulphuric  acid,  a  black  coloration  is  produced,  due  to  the 
formation  of  nitrosyl  ferrous  sulphate.  On  heating,  the  colour 
disappears,  and  the  ferrous  is  changed  to  \kzferric  sulphate. 

Note. — There  are  two  ways  of  applying  this  test : — 

(a)  Place  a  drop  or  two  of  the  solution  on  a  white  porcelain  slab  or  crucible  lid,  and 
having  added  a  drop  of  strong  sulphuric  acid,  put  a  small  and  clean  crystal 
of  the  ferrous  sulphate  in  the  liquid,  when  a  black  ring  will  gradually  form 
round  the  crystal. 

(£)  Place  the  solution  in  a  tube,  and  having  added  some  strong  solution  of  ferrous 
sulphate,  cautiously  pour  some  strong  sulphuric  acid  down  the  side  of  the 
tube,  so  that  it  sinks  to  the  bottom  by  reason  of  its  great  gravity  without 
mixing  with  the  fluid.  If  nitric  acid  be  present,  a  dark  line  will  be  formed 
at  the  junction  of  the  two  liquids. 

5.  Treated  with  sulphuric  acid,  and  a  few  drops  of  indigo  sulphate 

added,  the  blue  colour  of  the  latter  is  destroyed,  being  changed 
to  yellow  (not  characteristic).  3C]6Hi0N2O2  (!NDIGOTIN)  + 
4HNO3  =  6C8H5NO2  (ISATIN)  +  4NO  +  2H2O. 

6.  The  most  delicate  test  for  nitrates  is,  however,  phenol -sulphonio 

(sulpho-carbolic]  acid.  This  reagent  is  prepared  by  dissolving 
one  part  of  carbolic  acid  in  four  parts  of  strong  sulphuric  acid, 
and  then  diluting  with  two  parts  of  water.  A  few  drops  of  the 
solution  to  be  tested  are  evaporated  to  dryness  on  a  porcelain 
crucible  lid  over  the  water  bath,  and  while  still  over  the  bath 
a  drop  of  the  reagent  is  added,  when  a  reddish  colour  is  im- 
mediately produced,  owing  to  the  formation  of  nitro- phenol. 


40  DETECTION,   ETC.,    OF  ACID  RADICALS. 


21   CYANOGEN,  HYDROCYANIC  ACID,  and  CYANIDES. 

Cyanogen — (C2N2)  or  (Cy2) — is  a  colourless  gas,  which  is  recognised — 

1.  By  its  odour  of  bitter  almonds. 

2.  By  its  burning  in  the  air  with  a  peach-blossom-coloured  flame,  pro- 

ducing carbonic  anhydride  and  nitrogen. 

3.  By  forming  ammonium  oxalate  when  passed  into  water. 

Hydrocyanic  Acid — HCN — is  volatile,  soluble  in  water,  and  possesses  a 
characteristic  faint  sickly  odour  of  almonds.  Its  reddening  action  on  litmus 
paper  is  very  transient.  Its  tests  are  four  in  number,  as  follows : — 

1.  The  Silver  Test. — Argentic  nitrate  gives  a  curdy  white  precipitate 

of  argentic  cyanide.  The  precipitate  is  soluble  in  ammonium 
hydrate  and  in  strong  boiling  nitric  acid,  but  not  in  dilute 
nitric  acid ;  nor  does  it  blacken  on  exposure  to  the  light. 

2.  Scheetes  Iron  Test. — An  excess  of  solution  of  potassium  hydrate  is 

mixed  with  the  solution.  To  this  a  mixture  of  a  ferrous  and  a 
ferric  salt  is  added,  and  the  whole  acidulated  with  hydrochloric 
acid.  If  hydrocyanic  acid  be  present,  Prussian  blue  will  be 
formed. 

The  explanation  of  the  test  is  as  follows  (according  to  Gerhardt's  view)  : — 

(1)  The  hydrocyanic  acid  and  the  potassium  hydrate  form  potassium  cyanide. 

(2)  The  addition  of  the  ferrous  salt  produces  ferrous  cyanide. 

(3)  This  reacting  with  the  excess  of  alkali  forms  potassium  ferrocyanide. 

(4)  On  the  addition  of  the  ferric  salt,  it  is  at  first  precipitated  by  the  excess  of  alkali, 

as  ferric  hydrate,  which  on  acidulation  dissolves  to  ferric  chloride,  forming 
ferric  ferrocyanide  (Prussian  blue). 

(i.)  6HCN  +  6KHO  =  6KCN  -f  6H2O. 
(ii.)  6KCN  -f  3FeCl,  =  3Fe(CN)0  +  6KC1. 
(iii.)  3Fe(CN),  +  4KHO  =  K4Fe(CN)6  +  2Fe(HO),. 
(iv.)  3K4Fe(CN)6+2Fe,C]6=(Fe2)2(Fe(CN)6)3  +  "i2KCl. 
Or  the  whole  may  be  shown  in  one  equation,  thus  : — 

iSKCN  +  3FeCl2  +  2Fe2Cl6  =  (Fea)2(Fe(CN)6)3  +  18  KC1. 

3.  The  Sulphur  Test. — A  few  drops  of  yellow  ammonium  sulphydrate 

is  added,  and  the  whole  is  evaporated  to  dryness  at  a  very 
gentle  heat,  with  the  addition  of  a  drop  of  ammonium  hydrate. 
A  residue  is  thus  obtained  which  (when  cold)  strikes  a  blood- 
red  colour  with  ferric  chloride,  not  dischargeable  by  hydro- 
chloric acid,  but  at  once  bleached  by  solution  of  mercuric 
chloride. 

fhis  colour  is  due  to  the  formation  of  ammonium  thiocyanate  (which  takes  place 
when  an  alkaline  sulphide,  containing  excess  of  sulphur,  is  brought  into 
contact  with  cyanogen) — 

2HCN  +  (NH4),S  +  S2  =  2NH4CNS  +  H?S, 
and  subsequent  production  of  red  ferric  sulphocyanide. 

4  ScKSribMs  Test. — Filtering  paper  is  soaked  first  in  a  3  per  cent, 
alcoholic  solution  of  guaiacum  resin,  and  then  in  a  2  per  cent, 
solution  of  cupric  sulphate,  and  exposed  to  the  air.  When 
this  paper  is  either  moistened  with  the  suspected  solution  or 
exposed  to  its  vapour,  a  blue  colour  is  produced. 

Cyanides  are  known  (practise  upon  solution  of  potassium  cyanide — KCN) — 
i.   By  effervescing  and  giving  off  the  odour  of  hydrocyanic  acid  when 

heated  with  sulphuric  acid. 
•*    By  answering  to  all  the  tests  for  hydrocyanic  acid  above  mentioned. 

. — In  applying  the  silver  test  to  a  soluble  cyanide,  the  reagent  must  be  adde<) 
in  excess,  as  argentic  cyanide  is  soluble  in  alkaline  cyanides  to  form  double 


CYANATES  AND  FERROCYANIDES.  41 

cyanides  of  silver  and  the  alkali  used.  Excess  of  argentic  nitrate,  however, 
decomposes  these  compounds,  and  forms  insoluble  argentic  cyanide.  The 
previous  addition  of  a  slight  excess  of  dilute  nitric  acid  ensures  the  immediate 
separation  of  the  argentic  cyanide,  by  preventing  the  reaction  just  referred  to. 

3.  Insoluble  cyanides  yield  cyanogen  when  heated  per  se  in  a  small 
dry  test-tube,  the  open  end  of  which  has  been  drawn  out  into 
a  jet  after  the  introduction  of  the  cyanide.  The  application  of 
a  light  to  the  jet  gives  the  characteristic  flame  of  cyanogen. 

25.   CYANIC  ACID  and  CYANATES,  CYANTJRIC  ACID  and 
FULMINIC  ACID. 

Cyanic  Acid — HCNO — is  characterised — 

1.  By  being  a  colourless  liquid,  having  a  strong  pungent  odour,  greatly  resembling 

acetic  acid,  or  very  weak  sulphurous  acid,  and  forming  ammonium  bicar- 
bonate on  adding  water. 

2.  By  changing  into  a  white  solid  isomer  on  keeping,  heat  being  evolved,  but  no 

decomposition  occurring. 
Cyanates  are  known — 

1.  By  giving,   when  moistened,  a  bicarbonate.     (The  potassium  salt — KCNO — foi 

instance  forms  potassium  bicarbonate  — KHCO3.) 

2.  By  producing  urea  when  evaporated  with  an  ammonium  salt. 
Cyanuric  Acid  is  a  polymeric  modification  of  cyanic  acid,  which  is  recognised — 

1.  By  being  a  crystalline  solid,  yielding  cyanic  acid  on  applying  heat. 

2.  By  not  being  decomposed  by  strong  hot  HNO3  or  H2SO4. 

Fulminic  Acid  (intermediate  between  the  two  above  acids)  differs  from  both  by  the  fearful 
explosibility  of  its  salts. 

26.   THIOCYANATES  (Snlphocyanates). 

(Practise  upon  solution  of  potassium  thiocyanate — KCNS). 

Snlphocyanates  are  recognised — 

1.  By  evolving  hydrocyanic  acid  and  depositing  sulphur  on  heating 

with  sulphuric  acid. 

2.  By  producing  with  Fe2Cl6,  or  any  ferric  salt,  a  blood-red  solution 

of  ferric  thiocyanate — Fe2  (CNS)6 — not  destroyed  by  HC1  (dis- 
tinction from  acetate),  but  bleached  by  mercuric  chloride 
(distinction  from  meconate). 

27.  FERROCYANIDES 

(Practise  upon  solution  of  potassium  ferrocyanide — K4Fe(CN)6.) 

Ferrocyanides  are  mostly  insoluble  in  water,  except  those  of  the  metals  of  the 
first  and  second  groups.     They  are  characterised — 

1.  By  giving  off  hydrocyanic  acid  and  forming  a  deposit  on  heating 

with  diluted  sulphuric  acid. 

2.  By  giving  with   FeS04  or   any   ferrous   salt   a    white   precipitate 

of  potassium  ferrous. ferrocyanide — K2Fe(Fe(CN)6) — changing 
quickly  to  blue. 

3.  By  yielding  with  Fe  Clr>  or  any  ferric  salt  a  dark  blue  precipitate 

of  ferric  ferrocyanide— (^^(^^(C^}^— insoluble  in  HC1,  but 
turned  reddish-brown  by  KHO,  which  decomposes  it  into 
ferric  hydrate  and  potassium  ferrocyanide.  The  original  blue 
is  restored  by  adding  HC1. 

4.  Cupric  salts  produce  a  reddish-brown  precipitate  of  cupric  ferro- 

cyanide— Cu2Fe(CN)6 — insoluble  in  acids,  dissolved  by  NH4HO 
but  left  unaltered  on  evaporating  off  the  ammonia. 


42  DETECTION,   ETC.,    OF  ACID  RADICALS. 

5.  By  precipitating  white  plumbic  ferrocyanide  from  solutions  of  lead 

salts. 

6.  By  yielding  white  mercuric  ferrocyanide  with  a  mercuric  salt. 

7.  By  giving  a  white  gelatinous  precipitate  of  zinc  ferrocyanide  on  the 

addition  of  solutions  of  zinc  salts. 

8.  By  producing  with  argentic    nitrate — AgN03 — white    gelatinous 

silver  ferrrocyanide,  dissolved  by  NH4HO  on  heating. 

None  of  these  precipitates  can  be  produced  in  alkaline  solutions  ;  and  they  form 
best  in  slightly  acid  solutions. 

28.   FERRICYANIDES. 

(Practise  upon  solution  of  potassium  ferricyanide — K6Fe2(CN)12.) 

Most  ferricyanides  are  insoluble,  those  of  the  alkalies  and  of  the  barium 
group  being  exceptions.     They  are  recognised — 

1.  By  yielding  an  odour  of  hydrocyanic  acid,  and  a  deposit  on  heating 

with  diluted  sulphuric  acid. 

2.  By  producing  with  FeS04  or  any  ferrous   salt  dark-tinted   Turn- 

bults  blue — Fe3Fe2(CN)12 — insoluble  in  acids,  but  forming 
K6Fe2(CN)i2  when  boiled  with  KHO,  and  depositing  dirty 
green  Fe  (HO)2. 

3.  By  producing   no   precipitate   but   a  brownish    coloration    when 

added  to  Fe2Cl6  or  any  feme  salt  in  solution  (distinction  from 
ferrocyanide). 

4.  By  giving  no  precipitate  in  a  lead  solution  (another  distinction  from 

ferrocyanide). 

5.  By  throwing  down  mercurous  ferricyanide  of  a  brownish-red  colour 

from  a  mercurous  solution. 

6.  By  yielding  with  argentic  nitrate  solution  an  orange  precipitate  of 

argentic  ferricyanide  (another  distinction  from  ferrocyanide}. 

»9.  HYPOPHOSPHITES. 

(Practise  upon  solution  of  calcium  hypophosphite— Ca(PH2O2)2.) 

All  soluble  except  the  silver  salt.     The  following  reactions  serve  for  their 
detection : — 

1.  When  heated  in  a  solid  state,  they  take  fire,  evolving  phosphuretted 

hydrogen,  and  leaving  a  residue  of  pyrophosphate. 
Note. — This  must  be  done  on  porcelain,  as  they  destroy  platinum  foil. 

2.  With  argentic  nitrate  they  give  a  white  precipitate,  which  turns 

brown  owing  to  its  reduction  to  metallic  silver. 

3.  With  mercuric  chloride  they  yield,  when  slightly  acidulated  with 

HC1,  a  precipitate  of  calomel,  which,  on  heating,  turns  dark, 
owing  to  a  reduction  to  the  metallic  state. 

4.  After  removal  of  the  base,  the  free  hypophosphorous  acid,  when 

boiled  with  solution  of  cupric  sulphate,  will  give  a  deposit  of 
metallic  copper. 

5.  Treated   with   ammonium  molyldate — (NH4)_Mo04 — they   give    a 

fine  blue  precipitate.  As  afterwards  mentioned,  phosphates  give 
a  yellow,  and  consequently  when  the  solution  contains  both 
classes  of  salts  the  precipitate  is  green.  This  forms  an  excellent 
and  rapid  method  of  checking  any  commercial  sample  of 
hypophosphites. 


PHOSPHITES  AND   ORTHOPHOSPHATES.  43 

They  are  distinguished  from  phosphites  by  not  giving  precipitates  with 
neutral  barium,  or  calcium  chloride,  or  with  plumbic  acetate.  In  performing 
the  4th  reaction,  the  base,  if  calcium,  is  removed  by  oxalic  acid,  if  barium,  by 
sulphuric  acid,  and  if  a  heavy  metal,  by  sulphuretted  hydrogen. 

30.  PHOSPHOROUS  ACID— H3P03— and  PHOSPHITES 

are  distinguished  as  follows  : — 

1.  Heated  on  platinum  foil,  they  burn.     They  are  powerful  reducing  agents. 

2.  The  only  phosphites  soluble  in  water  are  those  of  K,  Na,  and  NH4,  but  acetic 

acid  dissolves  all,  except  plumbic  phosphite. 

3.  With  zinc  and  sulphuric  acid  (nascent  hydrogen)  they  yield  phosphuretted  hydro- 

gen, burning  with  an  emerald-green  colour,  and  throwing  down  Ag3P,  as  well 
as  Ag  from  AgNO3  in  solution. 

4.  They  give  precipitates  with  neutral  barium,  and  calcium  chlorides,  and  also  with 

plumbic  acetate,  which  hypophosphites  do  not. 

5.  Heated  with  mercuric  chloride  or  argentic  nitrate,  they  yield  a  precipitate  of 

metallic  mercury  or  silver. 

2HgCl2  +  2H3PO3  -I-  2H2O  =  2H3PO4  +  Hg2  +  4HC1. 
31.  META-  AND  PYRO-PHOSPHORIC  ACIDS  AND  THEIR  SALTS. 

Metaphosphoric  Acid — HP03 — is  a  glassy  solid,  not  volatile  by  heat.  It  is  freely  soluble  in 
cold  water,  and  is  converted  by  boiling  into  orthophosphoric  acid.  It  is  known  by  giving 
a  white  precipitate  with  ammonio-argentic  nitrate,  and  by  its  power  of  coagulating  albumen. 

Metaphosphates  are  known  by — 

1.  Giving  no  precipitate  with  ammonium  chloride,  ammonium  hydrate,  and  mag- 

nesium sulphate,  added  successively. 

2.  Giving  a  white  precipitate  of  argentic  metaphosphate — AgPO3 — with  argentic 

nitrate  only  in  neutral  solutions,  and  soluble  both  in  nitric  acid  and  am- 
monium hydrate. 

Pyrophosphoric  Acid — H4P207— is  also  soluble  in  water  and  convertible  by  boiling  into 
orthophosphoric  acid.  It  gives  a  white  precipitate  with  ammonio-argentic  nitrate,  but 
does  not  coagulate  albumen.  Pyrophosphates  are  insoluble  in  water,  except  those  of  the 
alkalies.  Their  tests  are  not  very  well  defined,  but  they  give — 

1.  A  white  precipitate  of  argentic  pyrophosphate  —  Ag4P2O7 — with  argentic  nitrate 

in  a  neutral  solution  only,  and  soluble  both  in  nitric  acid  and  ammonium 
hydrate. 

2.  (NH4)2MoO4  does  not  produce  an  immediate  precipitate. 

32.   ORTHOPHOSPHORIC  ACID  and  ORTHOPHOSPHATES. 

Orthophosphoric  acid — H3P04 — is  a  liquid  with  a  strongly  acid  reaction, 
converted  by  heat  first  into  pyro-  and  finally  into  meta-phosphoric  acid, 
which  remains  as  a  glassy  residue.  It  is — 

1.  Not  volatile  by  a  red  heat. 

2.  It  gives  a  yellow  precipitate  of  argentic  phosphate — AgsPO* — when 

treated  with  ammonio-argentic  nitrate,  soluble  both  in  nitric 
acid  and  ammonium  hydrate. 

Phosphates  are  as  a  rule  insoluble  in  water,  except  the  alkaline  ones.  They 
are  readily  soluble  in  dilute  acids,  and  entirely  reprecipitated  on  neutral- 
ising by  an  alkali  or  an  alkaline  carbonate.  Calcium,  strontium,  and  barium 
phosphates  are  only  partly  soluble  in  dilute  sulphuric  acid,  being  converted 
into  a  soluble  phosphate  and  an  insoluble  sulphate  of  the  metal.  If  the 
insoluble  sulphate  be  filtered  out,  the  addition  of  an  alkali  causes  only  a 
slight  precipitate  of  a  dimetallic  phosphate,  and  a  phosphate  of  the  alkali 
used  is  left  in  solution ;  but  it  is  only  after  the  use  of  sulphuric  acid  that 
any  phosphate  thus  remains  dissolved. 

Phosphates  are  detected  as  follows  (practise  on  solution  of  disodium-phos- 
phate— Na2HPO4)— 


44  DETECTION,   ETC.,    OF  ACID  RADICALS. 

1.  With  barium  or  calcium  chloride  white  precipitates  are  produced, 

soluble  in  acetic  acid  (distinction  from  oxalates]  and  all  stronger 
acids. 

2.  With  argentic  nitrate  a  lemon-yellow  precipitate  of  anrentic  phos- 

phate forms,  soluble  both  in  nitric  acid  and  ammonium  hydrate. 

3.  With  ferric  chloride  in  the  presence  of  ammonium  acetate  a  white 

precipitate  of  ferric  phosphate  appears,  insoluble  in  acetic  acid. 

4.  With  magnesia  mixture  phosphates  yield  a  white  crystalline  pre- 

cipitate, forming  slowly  in  dilute  solutions,  consisting  of  ammo- 
nium-magnesium phosphate — Mg(NH4)PO4  +  6H2O — soluble 
in  acetic  and  all  acids. 

5.  With  solution  of  ammonium  molybdate  in  nitric  acid  a  yellow 

precipitate  is  produced,  insoluble  in  nitric  acid,  but  soluble  in 
ammonium  hydrate. 

6.  With    uranic    nitrate — UrO.(NO3)2 — phosphates    yield   a   yellow 

precipitate  of  uranic  phosphate ',  also  insoluble  in  acetic  acid. 

7.  With  mercurous  and   bismuthous  nitrates  white  precipitates   are 

formed,  the  former  soluble  and  the  latter  insoluble  in  nitric 
acid. 

8.  With  any  soluble  salt  of  lead  a  white  precipitate  of  plumbic  phos- 

phate is  produced,  soluble  in  nitric  acid,  but  insoluble  in  acetic 

acid  or  ammonium  hydrate. 

Note. — Magnesia  mixture  is  made  by  dissolving  ordinary  magnesium 
carbonate  in  a  slight  excess  of  dilute  HC1,  then  adding  to  this  solution  g 
of  its  bulk  of  strong  NH4HO,  and  finally  stirring  in  solid  NH4C1  until  the 
precipitate  is  dissolved. 

33.  ARSENIOUS  ACID  and  ARSENITES. 

Arsenious  Acid— JLAs03— is  not  known  in  the  free  state;  but  its  anhydride 
— As2O3 — is  commonly  sold  as  arsenious  acid,  and  when— 

T.  Dropped  upon  red-hot  charcoal  or  coal,  or  heated  in  a  dry  tube 
with  black  flux  (or  a  mixture  of  dry  sodium  carbonate  and 
potassium  cyanide),  arsenic — As4 — is  set  free,  and  volatilises 
with  an  odour  of  garlic,  producing  a  steel-grey  mirror  on  the 
sides  of  the  tube. 

2.  Dissolved  in  water  only,  and  ammonio-argentic  nitrate  added,  a 

canary-yellow  precipitate  of  argentic  arsenite — Ag^AsO3 — is 
produced,  soluble  in  excess  of  either  NH4HO  or  HNO3. 

3.  A  pure  aqueous  solution,   mixed  with   ammonio-cupric   sulphate, 

gives  a  bright-green  cupric  arsenite — Scheele's  green — CuHAsO3 
—also  soluble  in  NH4HO  or  in  HNO3. 

4.  Any  solution  yields  all  the  reactions  for  arsenic  (see  page  15). 
Arsenites  behave  peculiarly  in  many  respects.     Ammonium  arsenite  leaves 

arsenious  acid  on  evaporating  a  solution,  while  potassium  and  sodium 
arsenites  possess  a  degree  of  alkalinity  which  no  excess  of  arsenious  acid 
will  disturb.  Ba,  Sr,  and  Ca  form  soluble  hydrogen  salts.  All  other 
arsenites  are  insoluble. 

Neutral  solutions  of  arsenites  are  possessed  of  the  undermentioned  distinctive 
peculiarities  : — 

1.  CuSO}  throws  down  greenish  cupric-hydrogen  arsenite. 

2.  AgN03  is  transformed  into  yellow  insoluble  argentic  arsenite. 

3.  H  S,  in  the  presence  of  hydrochloric  acid,  gives  a  yellow  precipitate  of 

arsenious  sulphide. 

4.  The  solution  gives  the  usual  reactions  for  arsenic  (see  page  15). 


ARSENIA1ES,   PERMANGANATES  AND   CHROMATES.       45 


34.  ARSENIC  ACID  and  ARSENIATES. 

Arsenic  Acid— H3As04 — is  known  by  the  following  characters  : — 

1.  The  crystals  are  deliquescent,  white,  and  strongly  acid.     Heated, 

they  leave  a  residue,  which,  on  moistening  with  water,  is  also 
acid. 

2.  It  is  strongly  corrosive  and  blisters  the   skin.     It  gives  brick  red 

Ag3AsO4  on  adding  ammanio-argentic  nitrate. 

Arseniates  behave  in  every  respect  exactly  like  phosphates,  except  that  they 
give  a  brick-red  precipitate  with  argentic  nitrate,  instead  of  a  yellow. 
Insoluble  arseniates  are  best  treated  by  boiling  with  NaHO,  filtering,  exactly 
neutralising  the  filtrate  with  dilute  HNO3,  and  then  getting  the  brick-red 
precipitate  with  AgNO3. 


35.  MANGANATES, 

Manganates  are  unstable  compounds,  and  only  the  alkaline  salts  dissolve  in  water,  forming 
green  solutions. 

1.  Soluble  manganates  decompose  spontaneously,  depositing  MnO^  the  green  colour 

changing  to  purple  or  reddish  violet,  owing  to  the  formation  of  a  perman- 
ganate, 

3K,MnO4  +  2HaO  =  2KMnO4  +  4KHO  +  MnO2. 

2.  Dilute  acids  effect  this  change  more  rapidly,  and  the  reaction  is  very  delicate. 

The  free  hydrate  is  then  replaced  by  a  salt  of  the  acid  used. 

3.  Strong,  heated  H.,SO4  acts  as  represented  in  this  equation  :  — 

K.,MnO4  +  2H,SO4  =  K?SO4  +  MnSO4  +  2H2O  +  O2. 

4.  Strong  HC1  causes  the  evolution  of  CL.     The  other  actions  are  similar  to  those 

of  permanganates,  but  less  energetic. 


36.  PERMANGANATES. 

(Practise  on  solution  of  potassium  permanganate — KMnO4.) 

Permanganates  are  known — 

1.  By  the  violet  colour  of  their  solutions,  which  is  entirely  bleached  by 

oxalic  acid  or  by  heating  with  hydrochloric  acid  and  dropping 
in  rectified  spirit. 
2KMnO4  +  5  H2C2O4  +  3H2SO4=K2SO4  +  2MnSO4  +  loCO^  +  8H2O. 

2.  By  giving  off  oxygen  on  heating. 

3.  By  giving  off  oxygen  when  heated  with  sulphuric  acid,  often  with 

explosive  violence. 

4.  By  evolving  chlorine  when  simply  mixed  with  hydrochloric  acid. 

5.  By  getting  the  reactions  for  manganese  after  reducing  with  HC1  and 

a  few  drops  of  alcohol. 

37.   CHROMIC  ACID  and  CHROMATES. 

Chromic  Acid — H.,Cr04 — not  being  capable  of  isolation,  is  represented  by 
its  anhydride— -CrO3.  This  is  a  dark  red  crystalline  solid,  giving  off  oxygen 
when  heated,  and  when  mixed  with  an  aqueous  solution  of  hydrogen  peroxide 
— (H2O2)— in  ether  a  deep  blue  liquid  results. 

This  test,  for  either  CrO3  or  H2O2,  is  exceedingly  delicate,  the  ethereal 
solution  of  perchromic  acid  separating  from  the  water  and  thus  concentrating 
the  colour  into  a  small  bulk  of  ether 


46  DETECTION,  ETC.,   OF  ACID  RADICALS. 

Chromates  of  the  alkalies  are  soluble,  while  those  of  the  other  metals  are 
chiefly  insoluble,  but  have  brilliant  yellow  or  red  colours.  They  are  very 
poisonous,  and  are  detected  as  follows  (practise  on  solution  of  KiCrO4  and 
K2Cr2O7  respectively) : — 

1.  Soluble  chromates  give  a  yellow  precipitate  with  plumbic  acetate 

or  barium  chloride,  soluble  in  nitric  acid,  insoluble  in  acetic 
acid.  The  lead  salt  is  darkened  in  colour  by  alkalies,  and  is 
freely  soluble  in  excess  of  hot  KHO. 

2.  With  argentic  nitrate  a  dark  red  precipitate,  also  soluble  in  nitric 

acid,  and  in  NH4HO,  but  not  in  acetic  acid. 

3.  Boiled  with  hydrochloric  acid  and  alcohol,  or  any  reducing  agent, 

they  turn  green,  owing  to  the  production  of  chromic  chloride. 

4.  Treated  with  sulphuretted  hydrogen,  in  the  presence  of  hydrochloric 

acid,  they  turn  green,  and  a  deposit  of  sulphur  takes  place  : — 
2K2Cr2O7  +  I6HC1  +  6H,S  =  2Cr2Cl«  +  4KC1  +  382  +  i4H2O. 

5.  Soluble  chromates  treated  with  an  acid  turn  orange ;  and  soluble 

dichromates,  when  treated  with  potassium  hydrate,  turn  yellow. 
In  this  way  they  are  mutually  distinguished. 

6.  Heated  with  strong  H2S04  they  give  off  oxygen. 

7.  Treated  with  an  excess  of   sulphuric   acid,  and  shaken  up  with 

solution  of  hydrogen  peroxide  in  ether,  they  give  a  gorgeous 
blue  colour. 


38.   STANNIC  ACID  and  STANNATES  (Stannites  ?). 

This  is  thrown  down  by  an  alkaline  hydrate  from  a  stannic  salt,  and  is  aho  produced  by  the 
action  of  nitric  acid  upon  tin. 

Stannates  are  formed  by  the  solution  of  the  acid  in  an  alkaline  hydrate,  and  are  detected  in 
the  examination  for  metals. 

Stannites  are  said  to  be  formed  by  the  solution  of  stannous  hydrates  in  an  alkaline  hydrate. 
They  decompose  on  boiling  with  KHO,  forming  stannates  and  throwing  down  metallic  tin. 


39.   ANTIMONIC  ACID 

Is  produced  by  the  action  of  nitric  acid  upon  antimony  as  a  white  powder.     Its  presence  is 
delected  during  the  examination  for  metals. 

40.   FORMIC  ACID  and  FORMATES. 

Formic  Acid— HCH02 — is  the  organic  acid  which  contains  the  highest 
percentage  of  oxygen,  and  approaches  most  nearly  in  composition  to  the 
supposititious  carbonic  acid — H2CO3.  It  is  a  tolerably  stable  liquid,  boiling  at 
the  same  temperature  as  water.  Formates  are  all  soluble  in  water,  and  behave 
as  follows  : — 

1.  Heated  to  redness  they  decompose  without  blackening. 

2.  Heated  with  H.,S04  they  evolve  CO,  which,  being  free  from  CO^, 

gives  no  effect  when  passed  through  lime-watert  but  burns  with 
the  usual  pale  blue  flame.     The  reaction  is — 

HCHO2  =  CO  +  H.O. 

3.  They  readily  reduce  argentic  nitrate,  when  boiled,  metallic  silver 

separating  as  a  mirror  on  the  tube. 


A  CRT  A  TES-  VA  LERIA  NA  TES—S  ULPHO  VINA  TES.  47 

41.  ACETIC  ACID  and  ACETATES. 

Practise  on  sodium  acetate — NaC2H3O2.) 

This  acid  is  characterised  by  its  odour  of  vinegar.  The  strong  acid  chars 
when  heated  with  strong  H2SO4. 

Acetates  are  all  soluble  in  water.  They  decompose  at  a  red  heat — if  the 
heat  rise  gently  and  the  mass  be  not  alkaline — yielding  acetone,  and  leaving 
a  carbonate,  oxide,  or  metal,  according  to  the  nature  of  the  basic  radical. 
When  heated  with  alkalies  marsh  gas— CH4 — is  evolved.  The  reaction  is  of 
this  type : — 

NaC2H302  +  NaHO  -  Na2CO3  +CH4. 

In  the  case  of  no  alkaline  hydrate  or  carbonate  being  present,  the  following 
is  an  example  of  the  effect  of  heat  on  acetates : — 

Ba(C2H3O2)2  =  BaCO3  +  C3H6O  (Acetone). 

Acetates  of  easily  reducible  metals,  such  as  copper,  yield,  when  heated,  a 
distillate  of  acetic  acid,  leaving  a  residue  of  the  metal,  or  in  some  cases  of 
oxide.  The  presence  of  acetates  is  analytically  determined  as  follows  : — 

1.  By  evolving  an  odour  of  acetic  acid  when  heated  with  sulphuric 

acid. 

2.  By  a  characteristic  apple-like  odour  of  acetic  ether — C2H5(C2H3O2) 

— which  they  evolve  when  heated  with  sulphuric  acid  and 
alcohol. 

3.  By  the  deep  red  colour  which  they   reduce  with  neutral  ferric 

chloride— ferric  acetate,  Fe2(C2H  P2)6— dis.  hargeable  by  both 
hydrochloric  acid  and  mercuric  chloride. 

42.  VALERIANIC  ACID  and  VALERIANATES. 

Valerianic  Acid— HC5H902— is  a  liquid,  which  is— 

Volatile,  malodorous,  colourless,  and  oily.     It  reddens  test-paper,  and 
dissolves  in  most  menstrua. 

The  general  characters  of  Valerianates  are : — 

1.  A  more  or  less  strong  odour  of  valerian  root  when  warmed  or 

moistened. 

2.  They  give,  when  heated  with  sulphuric  acid,  an  odour  of  valerian 

and  a  distillate  which,  on  the  addition  of  solution  of  cupric 
acetate,  forms,  after  the  lapse  of  some  time,  an  oily  precipitate ; 
gradually  solidifying,  by  the  absorption  of  water,  into  a  greenish- 
blue  crystalline  solid. 

43.  SULPHOVINATES  (Ethyl  sulphates). 

These    salts,   derived   from   ethyl  hydrogen   sulphate — C2H5HS04 — behave 
as  follows : — 

1.  Heated  with  strong  sulphuric  acid,  they  evolve  a  faint  ethereal 

odour. 

2.  They  give  no  precipitate  in  the  cold  with  barium  chloride;  but  on 

boiling,  a  white  precipitate  of  barium  sulphate  falls,  and  a  smell 
of  alcohol  is  perceived.  The  addition  of  a  little  solution  of 
barium  hydrate  after  the  chloride  and  before  boiling,  facilitates 
the  reaction ;  but  in  this  case  all  metals  precipitable  by  a  fixed 
alkali  must  first,  of  course,  be  removed. 

3.  Heated  to  redness,  they  leave  a  sulphate  of  the  metal. 


DETECTION,   ETC.,    OF  ACID  RADICALS. 


4.  Heated  with  sulphuric  acid  and  an  acetate,  or  with  strong  acetic 
acid,  they  evolve  acetic  ether  with  its  characteristic  odour  of 
apples. 

44.  STEARIC  ACID— HC18H3502-and  STEARATES. 

This  acid  is  distinguished  by  the  following  characters : — 

1.  A  white,  odourless,  fatty  solid,   melting  by  heat   and  soluble   in 

absolute  alcohol,  the  solution  having  an  acid  reaction. 

2.  Giving,  when  dissolved  in  KHO  and  the  solution  as  nearly  neutral- 

ised as  possible,  a  white  insoluble  precipitate  of  plumbic  stearate 
— Pb(C18H35O2)2 — on  the  addition  of  plumbic  acetate,  which  is 
insoluble  in  ether  (distinction  from  plumbic  oleate). 

Stearates  of  the  alkalies  are  alone  soluble  in  water. 

Any  stearate  heated  with  dilute  HC1  gives  the  free  acid,  which  floats 
as  an  oily  liquid,  solidifying  on  cooling  to  a  white  mass.  This 
test  is  applicable  to  the  analysis  of  soap  (hard,  containing  Na, 
or  soft,  in  which  K  is  present). 

45.  OLEIC  ACID  and  OLEATES. 

Oleic  Acid — HC]8H3302 — is  usually  an  oily  liquid,  but  remains  solid  below 
15°  C.  when  crystallised  from  alcohol. 

It  does  not  dissolve  in  water,  but  is  taken  up  by  ether  and  by  strong 
alcohol,  the  latter  solution  being  acid  in  reaction. 

Oleates  of  K  and  Na  alone  dissolve  in  water.     Acid  oleates  are  all  liquid  and 
soluble  in  cold  absolute  alcohol  and  ether. 

1.  They  do  not  separate  out  from  either  of  these  solvents  when  a  hot 

solution  is  cooled  (distinction  from  stearates  and  palmitates}. 

2.  Plumbic  oleate  is  precipitable  like  plumbic  stearate,  but  is  separated 

and  distinguished  from  it  by  dissolving  in  ether. 

46.  LACTIC  ACID— HC3H503— and  LACTATES. 

The  pure  strong  acid  resembles  glycerine  in  appearance,  liberates  hydrogen 
on  adding  zinc,  and  on  heating  takes  fire  and  burns  away  with  a  pale  flame, 
gradually  becoming  luminous.  It  dissolves  in  ether.  It  gives  pure  CO  when 
heated  with  sulphuric  acid.  Boiled  with  solution  of  potassium  permanganate 
it  gives  the  odour  of  aldehyd. 

Lactates  are  not  very  soluble  in  water.     They — 

1.  Are  insoluble  in  ether. 

2.  Argentic  lactate— AgC3H5O3 — when  boiled  gives  a  dark  precipitate, 

which  on  subsidence  leaves  a  blue  liquid. 

3.  Strong  solution  of  an  alkaline  lactate,  when  boiled  with  HgNO3, 

deposits  crimson  or  pink  mercurous  lactate — Hg2(C3H5O3)2. 

47.  OXALIC  ACID  and  OXALATES. 

(Practise  on  oxalic  acid — H.,C2O4— and  on  "  salts  of  sorrel.") 
The  acid  is  recognised  — 

1.  By  its  colourless  prismatic  crystals,  which  are  strongly  acid,  effloresce 

when  exposed  to  dry  air,  and  volatilise  on  heating  with  partial 
decomposition. 

2.  Ey  the  complete  discharge  it  effects  of  the  colour  of  a  solution  of 

potassium  permanganate  acidulated  with  dilute  H2S04. 


SUCCINA  TES—MALA  TES—TARTRA  TES  40 

3.  By  producing  free  H2S04  when  added  to  solution  of  CuS04.     (Thi.« 

is  one  of  the  very  rare  instances  in  which  SOi  is  replaced  by 
another  acid  radical  and  HJSO4  liberated.) 

4.  By  giving  the  reactions  of  an  oxalate. 

Oxalates  of  the  alkalies  are  soluble,  the  others  insoluble,  in  water.    Insoluble 
oxalates  dissolve  in  hydrochloric,  but  not  in  acetic  acid.    They  are  known  by — 

1.  Not  charring  when  heated,  but  only  turning  faintly  grey ;  followed 

by  a  sudden  glow  of  incandescence,  which  runs  through  the 
mass. 

2.  Not  charring  when  heated  with  sulphuric  acid,  but  yielding  CO  and 

CO2  with  effervescence. 

3.  Not  effervescing  with   cold  dilute  sulphuric  acid;    but   at   once 

liberating  CO2  with  effervescence  on  the  additon  of  a  pinch 
of  manganese  peroxide. 

4.  With  calcium  chloride  or  barium  chloride  in  a  neutral  or  alkaline 

solution,  they  give  a  white  precipitate  of  calcium  or  barium, 
oxalate,  insoluble  in  acetic  acid,  but  soluble  in  hydrochloric  add. 
(For  separation  of  oxalates  from  tartrates,  etc.,  see  No.  78.) 

48.  SUCCINIC  ACID— H2C4H404— and  SUCCINATES. 

This  acid  is  a  white  crystalline  solid.     It  is  known — 

1.  By  not  charring  with  strong  hot  sulphuric  acid. 

2.  By  subliming  in  a  tube  open  at  both  ends,  in  silky  needles,  without  giving  off  an 

irritating  vapour  (distinction  from  benzoic  acid). 

3.  By  burning,  when  heated  on  platinum,  with  a  blue  smokeless  flame. 
Succinates  are  recognised  as  follows  : — 

1.  With  ferric  chloride,  a  brownish-red  precipitate  Q{  ferric  succinate — Fe2(C4H4O4)3 

— is  formed. 

2.  With  hydrochloric  and  sulphuric  acids  no  precipitate  is  produced  (distinction  from 

benzoates}.  With  plumbic  acetate,  a  white  precipitate  of  plumbic  succinate, 
soluble  in  succinic  acid,  succinates,  and  plumbic  acetate. 

3.  Barium  succinate  is  soluble  in  hydrochloric  acid,  hence  no  effect  results  from  the 

addition  of  succinic  acid  to  barium  chloride  ;  but  on  the  further  addition  of 
alcohol  and  ammonium  hydrate,  a  white  precipitate  is  formed  (another  point 
0^ distinction  from  benzoates}. 

49.  MALIC  ACID  and  MALATES. 

Malic  Acid— H^C4H405 — is  a  colourless,  crystalline,  very  deliquescent  acid,  freely  soluble 
in  water  and  alcohol.     Acid  malates  are  most  stable.     The  characters  are  : — 

1.  Calcium  chloride,  added  to  a  neutral  solution  of  a  malate,  gives  no  precipitate. 

Alcohol,  however,  even  if  added  in  small  quantity,  throws  down  a  white 
precipitate  ;  and  boiling  aids  the  effect.  If  boiled  with  lime  water,  calcium 
malate  dissolves.  Calcium  citrate  is  insoluble. 

2.  Strong  I12SO4  gives  no  charring  for  some  time  (a  tartrate  is  carbonised  in  a  few 

minutes]. 

3.  Amorphous  plumbic  malate  fuses  below  100°  C.  in  water,  but  not  in  an  air-bath. 

50.  TARTARIC  ACID  and  TARTRATES. 

(Practise  upon  the  free  acid  and  also  upon  "  Rochelle  salt.") 
Tartaric  Acid — H2C4H406 — is  a  strong  acid,  soluble  in  water  and  spirit. 

1.  It  forms  usually  oblique  rhombic  prismatic  crystals,  of  an  acid  taste. 

2.  Heated  to  redness,  it  chars  and  finally  burns  away. 

3.  Heated  with  strong  H2S04,  it  blackens,  and  gives  the  odour  of  burnt 

sugar. 

4.  KC2H302  gives  a  white  precipitate  of  potassium  hydrogen  tartrate— 

KHC4H4OC — increased  by  the  addition  of  90  per  cent,  alcohol. 

5.  One  drop  of  solution  of  FeS04,  followed  by  a  few  drops  of  solution 

of  hydrogen  peroxide  and  an  excess  of  KHO,  gives  a  purple  or 
violet  colour. 


5C  DETECTION,   ETC.,    OF  ACID   RADICALS. 

The  same  compound  is  produced  on  adding  any  potassium  salt,  provided 
the  liquid  contain  excess  of  free  tartaric  acid  only. 

Tail-rates  of  the  alkalies  are  mostly  soluble ;  but  the  others  are  insoluble. 
The  acid  tartrates  of  K  and  (NH4)  are  nearly  insoluble.  Tartrates  are 
recognised  by  the  following  characters  : — 

1.  Heated  to  dull  redness  they  char  rapidly  and  give  off  a  smell  of 

burnt  sugar.  The  black  residue  contains  the  metal  as  car- 
bonate if  it  be  K,  Na,  Li,  Ba,  Sr,  or  Ca ;  but  the  tartrates  cf 
other  metals  usually  leave  the  oxides,  or  more  rarely  (as  in  th^ 
case  of  Ag2C4H4O6)  the  metal. 

2.  Heated  with  strong  sulphuric  acid,  they  blacken  rapidly,  and  give 

first  a  smell  of  burnt  sugar,  and  afterwards  evolve  S02. 

3.  Neutral  solutions  (free  from  more  than  a  trace  of  ammonium  salts) 

give,  on  adding  calcium  chloride,  a  white  precipitate  of  calcium 
tartrate^  which,  when  freed  from  other  salts  by  washing,  dissolves 
readily  in  cold  solution  of  potassium  hydrate,  but  is  again  pre- 
cipitated on  boiling.  The  precipitate  is  somewhat  soluble  in 
NH4C1,  but  not  in  NH4HO. 

4.  AgN03  yields  a  white  precipitate,  soluble  in  solution  of  ammonia  and  in 

nitric  acid.  The  ammoniacal  solution  is  reduced  on  heating,  and 
deposits  metallic  silver  as  a  mirror  on  the  sides  of  the  test  tube. 

5.  KC2H-02  gives  a  white  precipitate  in  moderately  concentrated  solu- 

tions when  acidulated  with  acetic  acid  and  well  stirred,  and 
especially  on  the  addition  of  90  per  cent,  alcohol. 

6.  If  to  the  solution  of  a  tartrate  acidulated  with  acetic  acid  be  added 

a  drop  of  solution  of  ferrous  sulphate,  then  a  few  drops  of 
solution  of  hydrogen  peroxide,  and  finally  an  excess  of  KIIO, 
a  purple  or  violet  colour  will  be  produced. 

51.  CITRIC  ACID  and  CITRATES. 

(Practise  upon  the  free  acid  and  upon  potassium  citrate.) 
t^itric  Acid — H3C6H507 — is  soluble  in  water  and  alcohol,  but  insoluble  in  pure 
ether.     It  entirely  burns  away  when  heated  to  redness  in  the  air ;  blackens 
slowly  when  heated  with  strong  sulphuric  acid;  and  when  neutralised  by 
ammonium  hydrate,  and  cooled,  the  solution  gives  no  precipitate  with  calcium 
chloride  until  it  has  been  boiled.     Added  to  ferric,  chromic,  or  aluminic 
salts  in  solution,  it  prevents  their  precipitation  by  ammonium  hydrate. 
titrates  exhibit  the  following  characters  : — 

i.  Heated  alone,  they  char  slowly,  and  evolve  an  odour  of  burnt  sugar, 
but  not  so  intense  as  that  of  a  tartrate.  At  a  dull  red  heat,  the 
citrates  of  K,  Na,  Li,  Ba,  Sr,  and  Ca  leave  their  carbonates  ; 
but  those  of  most  other  metals  leave  the  oxides.  Argentic 
citrate  leaves  the  metal. 

s.  Heated  with  strong  sulphuric  acid,  they  slowlv  blacken,  and  evolve 
a  slight  odour  of  burnt  sugar. 

3.  Mixed  in  the  cold  with  calcium  chloride,  in  the  presence  of  a  slight 

excess  of  ammonium  hydrate,  they  give  no  precipitate  ;  but  on 
boiling,  calcium  citrate — Ca^(C6H5O7)2 — separates  as  a  white 
precipitate.  If  this  precipitate  be  filtered  hot,  and  washed  with 
a  little  boiling  water,  it  is  found  to  be  quite  insoluble  in  cold 
solution  of  potassium  hydrate,  but  readily  soluble  in  neutral 
solution  of  cupric  chloride. 

4.  Mixed  with  argentic  nitrate  and  boiled,  no  mirror  of  metallic  silver 

is  produced. 


MECONA  TES—  CA  RB  OLA  TES—BENZOA  TES.  5 1 

52.  MECONIC  ACID  and  MECONATES. 

Meeonic   Acid — H2C7H2073H20—  is   a   white   powder,   with   a   strongly  acid 

reaction,  soluble  in  water,  alcohol,  and  ether,  and  giving  the  reaction  for 

meconates. 
Meconates  communicate  a  red  colour  to  ferric  chloride  solution.     This  colour 

is  not  discharged  by  HgCl^  but  is  bleached  by  dilute  HCl  (distinction  from 

a  sulpho-cyanaie). 

53.  CARBOLIC  ACID  (or  Phenol)— C6H5HO— and  CARBOLATES  (Phenates). 

The  qualities  of  this  body  are  very  distinctive. 

1.  It  is  a  colourless,  crystalline  solid,  melting  at  not  lower  than  33°  C., 

and  not  volatile  at  100°  C.,  having  the  odour  and  taste  of 
creasote,  being  very  poisonous,  and  not  reddening  blue  litmus 
paper. 

2.  The  crystals  deliquesce  readily,  forming  a  liquid  which  does  not 

mix  freely  with  water,  but  is  soluble  in  all  proportions  in  alcohol, 
ether,  and  glycerine. 

3.  Mixed  with  HCl  and  exposed  to  the  air  on  a  strip  of  deal,   it 

becomes  greenish  blue. 

4.  It  coagulates  albumen.     It  does  not  rotate  polarised  light. 

5.  Saturated  with  ammonia  gas — NH3 — and  heated  in  a  closed  tube, 

aniline  is  formed : — 

C6H5HO  +  NH3  =  C6H5H2N  +  H2O. 

6.  It  does  not  decompose  carbonates. 

7.  NH4HO  and  CaOCL,,  or  Na2OCl2,  produce  a  blue  liquid,  turned  red 

by  acids. 

8.  It  unites  directly  with  strong  H2S04  to  form  phenol-sulphonic  (or 

sulpho-carbolic]  acid. 

9.  With  bromine  water  it  gives  a  white  precipitate  of  tribromophenol 

— C6H3Br30. 
Carlolates  give  the  following  reactions  : — 

1.  When  heated  alone,  they  evolve  the  odour  of  carbolic  acid  and 

decompose. 

2.  Heated  with  strong  sulphuric  acid  they  also  smell  of  carbolic  acid. 

3.  Ferric  chloride  causes  a  reddish-violet  colour. 
Sulpho-Carbolates  behave  similarly,  but,  after  fusion  with  KN03  and  redis- 

solving  the  residue  in  diluted  HCl,  they  also  give  the  reactions  of  a  sulphate 
with  barium  chloride. 

54.   BENZOIC   ACID  and  BENZOATES. 

Benzoic  Acid — HC7H50., — is  of  characteristic  appearance,  being  usually  seen 
in  light,  feathery,  flexible,  nearly  colourless  crystalline  plates  or  needles,  and 
containing  a  trace  of  an  agreeable  volatile  oil,  unless  it  is  the  artificial  acid 
prepared  from  naphthalene,  when  it  is  odourless. 

1.  It  is  only  slightly  soluble  in  water,  but  dissolves  in  three  parts  of 

alcohol,  and  in  solutions  of  soluble  hydrates. 

2.  Heated   in   the  air,  it  burns  with  a  luminous  smoky  flame  ;  and 

when    made   hot    in   a   tube  open  at  both  ends,  sublimes  in 
needles,  giving  off  an  irritating  vapour. 
Benzoates  possess  the  following  general  qualities : — 

r.  Heated  with  sulphuric  acid  they  evolve  the  odour  of  benzoic  acid, 

and  darken. 

2.  Ferric  chloride,  in  a  solution  made  slightly  alkaline  by  ammonium 
hydrate,  gives  a  reddish-white  precipitate — ferric  benzoate — 


DETECTION,  ETC.,    OF  ACID  RADICALS. 


Fej(C7H5O2)6 — soluble  in  acids  (benzole  included)  If  this  pre- 
cipitate be  now  filtered  out  and  digested  in  ammonium  hydrate, 
it  is  decomposed  into  a  precipitate  of  ferric  hydrate,  and  a 
solution  of  ammonium  benzoate,  which  is  separated  by  filtration 
and  treated  as  in  3. 

3.  Strong  hot  solutions  of  benzoates  yield  crystals  of  benzole  add  when 
hydrochloric  acid  is  added  and  the  solution  allowed  to  cool. 

55.   SALICYLIC  ACID  (HC7H503). 

This  acid  occurs  in  prisms,  when  crystallised  from  a  solution  in  alcohol  in 
which  it  is  readily  soluble.  It  is  freely  dissolved  by  hot  water,  but  not 
readily  by  cold,  requiring  1,800  parts  of  the  latter  to  completely  dissolve  it. 

1.  Its  aqueous  solution  gives  with  ferric  chloride  a  deep  violet  coloration. 

The  compounds  with  methyl,  ethyl,  etc.,  give  this  reaction,  as 
well  as  the  ordinary  salts. 

2.  Its  methyl  ether,  formed  by  warming  a  salicylate  with  sulphuric 

acid  and  wood  spirit  has  the  odour  of  oil  of  wintergreen. 
From  most  other  solid  bodies  it  may  be  separated  by  taking  advantage  of 
its  exceptionally  great  solubility  in  ether.     In  the  event  of  its  presence  in 
an  organic  liquid  (such  as  milk),  it  or  its  salts  may  be  procured  in  a  pure 
condition  by  dialysis. 

56.   TANNIC,  GALLIC,  and  PYROGALLIC  ACIDS. 
Tannic  Acid — C27H22017 — is  soluble  in  water  and  alcohol,  and  very  soluble 

in  glycerine.     It  is  insoluble  in  pure  dry  ether,  but  dissolves  readily  in 

ether  containing  a  little  water. 
Gallic  Acid — H^C-H^OgHcjO — is  slightly  soluble  in  cold  water,  but  readily  in 

boiling ;  it  is  also  freely  soluble  in  glycerine,  and  slightly  in  alcohol 

and  ether. 
Pyrogallic   Acid — C6H6Oa — is   very   soluble   in  water,   the   solution   rapidly 

absorbing  oxygen  from  the  air  and  becoming  brown.     It  also  dissolves 

in  alcohol  and  ether. 

DISTINCTION  BETWEEN  GALLIC,  TANNIC,  AND  PYROGALLIC  ACIDS. 


BEHAVIOUR  OF  THE 
ACID  WITH 

GALLIC. 

TANNIC. 

PYROGALLIC. 

Ferrous  salts  — 

A  dark  solution 

The  same  effect 

A  blue  solution. 

FeS04. 

is  formed, 

as  Gallic. 

gradually  de- 

positing a 

precipitate. 

Ferric  salts  — 

Purplish      pre- 

Same   as    pre- 

A red  solution. 

Fe2Clfl. 

cipitate      im- 

ceding. 

mediately 

formed. 

Calcium    hydrate 

A  brownish  pre- 

A white   preci- 

Instantaneous 

—  Ca(OH)2  — 

cipitate,     be- 

pitate  slowly 

production    of 

in  the  form  of 

coming  deep 

changing. 

a  purple  solu- 

Milk of  Lime. 

brown    in    a 

tion  becoming 

few  seconds. 

brown  by  oxi- 

dation. 

Gelatine    .     .     . 

No    precipitate 

Immediate 

No  precipitate. 

(except  in  the 

brownish 

presence      of 

precipitate. 

\ 

gum). 

1 

CHL  ORIDES—BR  OMIDES— IODIDES.  53 

57.  SEPARATION  OF  CHLORATES  AND  CHLORIDES. 

Note.—  The  tests  which  follow  are  applicable  to  tests  for  adulterations,  where,  for  obvious 
reasons,  the  confirmatory  test  for  a  suspected  adulterant  would  not  apply. 

(Practise  on  mixed  solutions  of  KC1  and  KC1OE.) 

Add  excess  of  argentic  nitrate,  filter  out  the  argentic  chloride  formed,  and 
then  acidulate  with  sulphuric  acid,  and  drop  in  a  fragment  of  zinc,  when,  if  a 
chlorate  be  present,  a  second  precipitate  of  argentic  chloride  will  form. 

58.  DETECTION  OF  CHLORIDES  IN  THE  PRESENCE  OF  BROMIDES. 

(To  be  practised  on  a  mixture  of  KC1  and  KBr.) 

The  solution  is  divided  into  two  parts,  in  one  of  which  the  bromide  is 
proved  by  the  addition  of  chlorine  water,  and  shaking  up  with  chloroform. 
The  second  portion  is  either  (i)  Evaporated  to  dryness,  the  residue  placed 
in  a  tube  retort  with  a  little  potassium  dichromate  and  sulphuric  acid,  while 
into  the  receiver  is  placed  a  little  dilute  ammonium  hydrate,  and  distillation  is 
proceeded  with,  when,  if  a  chloride  be  present,  the  liquid  in  the  receiver  will 
be  coloured  yellow ;  or  (2)  Precipitated  with  excess  of  AgNO3,  washed  on 
a  filter,  percolated  with  dilute  NH4HO  (i  in  20)  and  nitric  acid  added  to  the 
percolate,  when  a  distinctly  curdy  white  precipitate  proves  the  presence  of 
chlorides.  This  latter  method  is  simple,  and  rarely  fails  if,  on  adding  the 
acid,  a  mere  cloud  be  disregarded. 

59.  DETECTION  OF  BROMIDES  IN  THE  PRESENCE  OF  IODIDES. 

(Practise  on  a  mixture  of  KBr  and  KI.) 

Add  to  the  solution  a  very  small  quantity  of  starch  paste  and  then  a  drop 
or  two  of  chlorine  water,  when  a  blue  colour  will  be  produced,  proving  the 
iodide.  Continue  to  add  more  chlorine  water  until  this  blue  is  entirely  dis- 
charged, and  then  shake  up  with  chloroform,  when,  if  a  bromide  be  present, 
the  characteristic  golden  colour  will  be  communicated  to  the  chloroform. 

60.  DETECTION  OF  CHLORIDES  IN  THE  PRESENCE  OF  IODIDES. 

(Practise  on  a  mixture  of  KC1  and  KI.) 

Add  excess  of  argentic  nitrate,  warm,  pour  off  the  supernatant  liquid,  wash 
•with  warm  water,  and  shake  up  the  precipitate  in  dilute  solution  of  ammonium 
hydrate  (i  in  3).  The  argentic  iodide  will  remain  insoluble,  while  the  chloride 
will  dissolve  and  may  be  detected  in  the  solution,  after  filtration,  by  reprecipita- 
•tion  with  excess  of  nitric  acid.  As  argentic  iodide  is  not  absolutely  insoluble 
in  ammonium  hydrate,  a  mere  cloud  on  adding  the  nitric  acid  is  to  be  dis- 
regarded. This  test  is  only  accurate  in  the  insured  absence  of  a  bromide, 
proved  as  above  directed  (see  59). 

61.  SEPARATION  OF  AN  IODIDE  FROM  A  BROMIDE  AND  CHLORIDE. 

(Practise  on  a  mixture  of  KC1,  KBr,  and  KI.) 

1.  Add  to  the  solution  a  mixture  of  one  part  cupric  sulphate  and  three  parts 

ferrous  sulphate,  or  mix  the  solution  with  excess  of  cupric  sulphate  and 
drop  in  sulphurous  acid  till  precipitation  ceases.  The  io.lide  will  separate 
as  cuprous  iodide — CuJ.,—  leaving  the  bromide  and  chloride  in  solution. 
Unless  carefully  done,  this  separation  is  not  absolutely  accurate,  or— 

2,  Add  to  the  solution  palladious  nitrate  until  precipitation  ceases.     Filter  out  the 

palladious  iodide  which  separates,  and  pass  sulphuretted  hydrogen  through 
the  liquid  to  remove  excess  of  palladium,  and  again  filter.  Boil  to  expel  t^ 
excess  of  H2S,  and  the  bromide  and  chloride  remain  in  solution. 


54  DETECTION,   ETC.,    OF  ACID  RADICALS. 

62.  DETECTION  OF  AN  IODATE  IN  AN  IODIDE. 

(Practise  on  a  solution  of  iodine  in  heated  potassium  hydrate — KI  -f  KIO3.) 

When  excess  of  tartaric  acid  is  added  to  potassium  iodate,  iodic  acid  is  set 
free;  and  when  the  same  acid  is  added  to  potassium  iodide,  hydriodic  acid 
is  set  free,  and  potassium  hydro-tartrate  formed.  Thus : — 

5KI  +  KIO3  +  6H,C4H4O6  =  sHI  +  HIO3  -f  6KHC4H4O6. 

If  these  acids  be  thus  liberated  together,  they  immediately  decompose, 
forming  water  and  free  iodine  : — 

5HI  +  HI03  =  3I2  +  3H20. 

If  therefore  starch  paste  and  tartaric  acid  be  added  to  pure  potassium 
iodide  no  coloration  takes  place,  because  only  hydriodic  acid  is  liberated; 
but  if  the  sample  contains  potassium  iodate,  an  immediate  production  of 
free  iodine  ensues,  which  turns  the  starch  blue. 

63.  DETECTION    OF   A   SOLUBLE    SULPHIDE    IN   PRESENCE   OF   A 
SULPHITE  AND  A  SULPHATE. 

(Practise  on  mixed  solutions  of  Na2S,  Na2SO3,  and  Na2SO4.) 
Pour  the  solution  on  a  little  cadmium  carbonate — CdCO3 — filter,  and  treat 
the  insoluble  matter  with  acetic  acid  to  remove  any  unacted-upon  cadmium 
carbonate.  If  a  sulphide  has  been  present,  a  yellow  residue  of  cadmium 
sulphide  will  remain  insoluble  in  the  acetic  acid,  while  cadmium  sulphite  and 
sulphate  will  be  found  in  the  first  filtrate,  if  these  two  radicals  were  present. 

61  SEPARATION  OF  THIOSULPHATES  FROM  SULPHIDES. 

(Practise  on  solution  of  commercial  hyposulphite  of  soda,  to  which  a  drop  of 
NH4HS  has  been  added.) 

Having  obtained  a  good  preliminary  idea  by  heating  with  H2SO4,  add  to 
a  portion  of  the  original  solution — ZnSO4 — in  excess,  and  filter. 

(a)  Precipitate  white,  and  soluble  in  HC1,  with  smell  of  H2S. 

=  Sulphides. 

b)  A  portion  of  filtrate  heated  with  H2SO4  deposits  S  and  smells  of 
SO-2 ;  and  another  portion  added  to  a  drop  or  two  of  ammonio- 
cupric  sulphate  instantly  causes  decolorisation. 
=  Hyposulphites. 

65.  SEPARATION  OF  SULPHIDES,  SULPHITES,  and  SULPHATES. 

(Practise   on   mixed  solutions  of  sodium  sulphite  and  sulphate,  to  which  a 
drop  of  NH4HS  has  been  added.) 

Pour  the  solution  on  an  excess  of  cadmium  carbonate,  digest  at  a  gentle 
heat,  filter,  and  examine  the  precipitate  for  a  sulphide  as  already  directed  (63). 
The  filtrate,  which  may  contain  the  sulphite  and  sulphate,  is  precipitated  by 
barium  chloride,  the  insoluble  precipitate  filtered  out  and  boiled  with  a  little 
hydrochloric  acid,  which  will  dissolve  the  barium  sulphite  with  evolution 
of  sulphurous  anhydride — SO2 — and  leave  the  barium  sulphate  insoluble. 

66.   SEPARATION    OF    SILICIC    ANHYDRIDE    (SILICA)   FROM    ALL 

OTHER  ACIDS. 

(Practise  upon  powdered  glass.) 

Fuse  the  substance  with  a  large  excess  of  KNaCO3  in  a  platinum  crucible, 
and  when  all  action  has  ceased,  cool,  and  boil  the  residue  with  water.  The 


QUALITATIVE  SEPARATION  OF  NITRITES,  IODIDES,  ETC.  55 

silica  passes  into  solution  with  the  other  acid  radicals,  and  the  metals  are  left 
as  oxides.  Acidulate  the  solution  with  hydrochloric  acid,  evaporate  to  dry- 
ness,  and  heat  the  residue  to  140°  C.,  and  maintain  the  heat  for  some 
time.  Drench  the  residue  with  strong  hydrochloric  acid,  then  add  water, 
and  boil,  when  the  silica  will  alone  remain  insoluble. 

67.  DETECTION  OF  A  NITRITE  IN  THE  PRESENCE  OF  A  NITRATE, 

Add  a  little  potassium  iodide  and  starch  paste,  and  acidulate  with  acetic 
acid,  when,  if  a  nitrite  be  present,  a  blue  colour  will  be  produced,  due  to 
the  liberation  of  iodine. 

68.  DETECTION  OF  FREE  NITRIC  ACID  IN  THE  PRESENCE  OF  A 

NITRATE. 

Digest  with  excess  of  barium  carbonate ;  filter,  and  add  to  the  filtrate  some  dilute  sulphuric 
acid,  when,  if  the  free  acid  is  present,  a  precipitate  of  barium  sulphate  will  be  produced. 
This  test  is  only  good  in  the  insured  absence  of  any  other  acid  capable  of  dissolving  barium 
carbonate.  It  will  also  serve  for  detecting  free  hydrochloric  and  acetic  acids  in  presence  of- 
their  salts. 

69.  DETECTION  OF  A  NITRATE  IN  THE  PRESENCE  OF  AN  IODIDE. 

The  fact  that  the  addition  of  strong  sulphuric  acid  liberates  iodine  renders 
the  proof  of  a  nitrate  by  the  ordinary  iron  process  doubtful  in  the  presence 
of  iodides  and  bromides.  In  this  case  boil  with  excess  of  KHO  until  any 
ammonium  salts  are  decomposed,  then  add  a  fragment  of  zinc  and  again  boil. 
Any  nitrate  present  will  be  converted  into  ammonia,  which  may  be  recognised 
in  the  steam  with  moistened  red  litmus  paper. 

70.  SEPARATION   OF  CHLORIDES,  IODIDES,   and  BROMIDES  FROML 

NITRATES. 

Digest  with  argentic  sulphate,  which  will  precipitate  the  halogens  as  silver 
salts  and  leave  the  nitrate  in  solution. 

71.  SEPARATION  OF  CYANIDES  FROM  CHLORIDES. 

Acidulate  slightly  with  HNOs,  add  excess  of  AgNO3,  wash  the  precipitate 
with  boiling  water,  and  boil  it  with  strong  nitric  acid,  when  the  AgCN  is 
decomposed,  leaving  the  chloride  insoluble.     The  solution  is  diluted  and  HCL 
added,  when  a  white  precipitate  indicates  dissolved  cyanide. 

72.  SEPARATION  OF  FERRO-  FROM  FERRI-CYANIDES. 

Acidulate  with  HC1,  add  excess  of  Fe2Cl6,  warm  gently ;  the  ferrocyanide- 
will  be  precipitated.  Pour  off  some  of  the  brownish  liquid  and  heat  with  a 
little  zinc  amalgam,  when  a  blue  precipitate  indicates  ferricyanide. 

73.  DETECTION  OF  CYANIDES  IN  THE  PRESENCE  OF  FERRO- 
AND  FERRI-CYANIDES. 

Acidulate  slightly  with  HNOs,  and  add  an  excess  of  a  mixture  of  ferrous 
and  ferric  sulphates,  and  warm  gently.  Pour  off  a  little  of  the  supernatant 
liquid,  add  excess  of  KHO,  and  then  acidulate  with  HC1,  when  the  production 
of  another  blue  precipitate  proves  cyanide. 


56  DETECTION,   ETC.,    OF  ACID  RADICALS. 


74.  DETECTION  OF  A  PHOSPHATE  IN  THE  PRESENCE  OF  CALCIUM, 
BARIUM,  STRONTIUM,  MANGANESE,  AND  MAGNESIUM. 

Dissolve  in  water  by  the  aid  of  the  smallest  quantity  of  nitric  acid,  then  add 
excess  of  ammonium  acetate ;  then  add  Fe2Cl  and  warm,  when  a  white  pre- 
cipitate of  ferric  phosphate — Fe.,(PO4)2 — will  form,  insoluble  in  the  acetic 
acid  liberated. 

75.  DETECTION  OF  A  PHOSPHATE  IN  THE  PRESENCE  OF  IRON. 

Dissolve  in  the  smallest  possible  quantity  of  hydrochloric  acid,  add  some 
citric  acid,  followed  by  excess  of  ammonium  hydrate,  and  lastly  cool  and  add 
magnesia  mixture,  when  a  white  precipitate  proves  phosphate. 

76.  SEPARATION  OF  AN  ARSENIATE  FROM  A  PHOSPHATE. 

Acidulate  with  HC1,  and  pass  a  slow  stream  of  H2S  for  several  hours,  until 
the  whole  of  the  arsenic  is  removed. 

77.    DETECTION   OF   A    FORMATE   IN   THE   PRESENCE    OF    FIXED 
ORGANIC  ACIDS  WHICH  REDUCE  SILVER  SALTS. 

Distil  with  dilute  H2SO4,  neutralise  the  distillate  with  Na.2CO3,  add  a  slight 
excess  of  acetic  acid,  and  boil  with  AgNO3,  when  a  dark  deposit  of  metallic 
•silver  will  form. 

78.   SEPARATION   OF   OXALATES,   TARTRATES,   CITRATES,   AND 

MALATES. 

If  the  solution  be  acid,  neutralise  it  with  sodium  hydrate ;  but  if  neutral  or 
alkaline  it  is  ready  for  use,  and  is  treated  as  follows  : — 

A.  Acidulate  slightly  with  acetic  acid,  boil  and  add  CaCl2  till  precipi- 

tation ceases.  Keep  warm  till  the  precipitate  aggregates,  and 
filter.  This  precipitate  is  calcium  oxalate,  and  it  should  be 
quite  insoluble  in  cold  solution  of  KHO. 

B.  To  filtrate  from  A,    mixed  with  some  more  CaCl2,  ammonia   is 

added  in  slight  excess,  and  the  whole  thoroughly  cooled. 
Calcium  tartrate  precipitates  and  the  liquid  is  poured  off  and 
preserved  for  C.  This  precipitate,  after  washing,  should  be 
soluble  in  cold  KHO,  and  reprecipitable  by  boiling. 

C.  The  liquid  is  slowly  boiled  for  some  time ;  and  if  a  precipitate 

does  not  form  readily,  a  little  more  CaCl2  and  NH4HO  is  added, 
and  the  boiling  resumed.  The  precipitate  is  filtered  out 
whilst  still  hot.  It  should  be  (after  washing)  quite  insoluble  in 
cold  KHO,  but  soluble  in  neutral  solution  of  CuCl2. 

D.  To  the  filtrate  add  alcohol,  when  calcium  malate  will  separate  ; 

but  this  portion  of  the  separation  is  not  infallible,  and  the 
precipitate  must  be  carefully  examined  to  see  that  it  really  is 
malate. 


79.  DETECTION   OF   PHENOL  IN   SALICYLIC   ACID. 

Dissolve  i  gram  in  excess  of  a  cold  solution  of  Na2COs ;  then  shake  up 
with  ether,  separate  the  latter  and  allow  it  to  evaporate,  when  any  phenol  will 
be  left  as  a  residue  from  the  ether. 


QUALITATIVE  SEPARATION  OF  ORGANIC  ACIDS,   ETC.   57 


80.  TEST   FOR   CINNAMIC  ACID   IN   PRESENCE   OF  BENZOATES. 

The  mixture  warmed  with  its  own  weight  of  K2Mn2O8  and  excess  of  diluted 
H2SO4  gives  the  odour  of  benzaldehyd  (oil  of  bitter  almonds)  if  a  cinnamate 
be  present. 

81.   TEST  FOR  CHLOROBENZOIC  ACID  IN  THE  PRESENCE  OF 

BENZOIC   ACID. 

•5  grm.  is  heated  in  a  closed  crucible  with  its  own  weight  of  CaCOa,  and 
the  resulting  mass  having  been  dissolved  in  diluted  nitric  acid,  a  white  pre- 
cipitate will  be  produced  on  adding  AgNOs  if  the  chloro-acid  be  present,  A 
mere  cloud  must  be  disregarded. 

82.  TEST  FOR  HIPPURIC  ACID  IN  BENZOIC  ACID. 

•2  grm.  suspended  in  10  c.c.  of  water  will  immediately  discharge  the  colour 
of  2  drops  of  a  i  per  cent,  solution  of  K2Mn2Os  when  this  impurity  is  present. 
A  similar  effect  is  produced  by  cinnamic  acid. 

83.  TEST  FOR   CRESOL  IN  PHENOL. 

One  volume  of  phenol  (carbolic  add),  liquefied  by  the  addition  of  10  per  cent, 
of  water,  should  form  a  perfectly  clear  solution  with  an  equal  volume  of 
glycerine  ;  if  not,  then  cresol  (cresylic  acid)  is  present. 

84.    SPECIAL   TESTS   FOR  THE  PRESENCE   OF   TARTARIC  ACID 

IN   CITRIC  ACID. 

(1)  One  drop  of  solution  of  FeSOi  with  a  few  drops  of  H2O2  and  an 

excess  of  KHO  added  to  a  solution  of  citric  acid  gives  a  violet 
or  purple  colour  if  tartaric  acid  be  also  present. 

(2)  One  gram  of  citric  acid  shaken  with  5  c.c.  solution  of  ammonium 

molybdate  and  3  drops  H2O2  and  placed  in  boiling  water  for 
10  minutes  becomes  bluish  if  tartaric  acid  be  present.  This 
test  can  also  be  simulated  by  the  presence  of  any  metallic 
particles  in  the  sample. 

85.  DISTINCTION   OF  SALICYLATES  FROM  CARBOLATES  AND 
SULPHOCARBOLATES. 

Any  solution  of  a  salicylate  if  not  weaker  than  i  per  cent,  gives  a  yellowish- 
brown  precipitate  with  uranic  nitrate,  while  carbolates  and  sulph*  carbolates 
do  not.  In  testing  salicylic  acid  it  should  be  first  dissolved  in  solution  of 
ammonium  citrate,  acetate,  or  borax. 

86.  TESTS  FOR   SELENIUM  IN   SULPHURIC  ACID. 

If  a  solution  of  Na^SOs  in  HC1  be  gently  poured  on  the  surface  of  FLSO4 
a  red  colour  will  be  produced  at  the  junction  of  the  two  liquids  in  presence  of 
selenium. 


CHAPTER    IV. 

QUALITATIVE  ANALYSIS,  AS  APPLIED  TO  THE  DETECTION 
OF  UNKNOWN  SALTS. 

§  I.  GENERAL  PRELIMINARY  EXAMINATION. 

UNDER  this  head  are  included — 

1.  The  observation  of  the  physical  properties  of  the  substance  sub- 

mitted for  analysis. 

2.  Its  behaviour  when  heated,  either  alone  or  in    the    presence    of 

reducing  agents  or  fluxes. 

3.  Its  reaction  with  test-papers ;  the  colour  it  communicates  to  flame, 

etc. 

So  particular  and  minute  may  this  examination  be,  that  in  the  larger  works 

on  chemical  analysis  many  pages  will  be  found  devoted  to  it ;  but  for  the 

purposes  of  the  analysis  likely  to  come  before  the  ordinary  chemical  student, 

it  is  sufficient  only  to  carry  it  the  length  of  a  few  readily  obtainable  and 

unmistakable  inferences.     It  should  also  be  remembered  that  in  many  cases  these 

inferences   require  subsequent  confirmation,  and  therefore  a  student  should  be 

taught  not  to  jump  too  readily  at  conclusions  from  the  preliminary  investigation. 

Step  1.     If  the  substance  be  a  liquid,  carefully  mark  its  reaction  with  blue 

and  red  litmus  paper,  evaporate  a  little  to  dryness  at  a  gentle  heat 

on  a  clean  porcelain  crucible  lid,  observing  the  nature  of  the  residue 

left,  if  any ;  and  finally  raise  this  residue  to  a  red  heat,  carefully 

noting  whether  it  is  volatilised,  blackened,  or  altered  in  colour  any 

way.     If  a  solid,  heat  it  directly  to  redness  on  a  crucible  lid  (or  in 

a  dry  test  tube),  and  note  effect ;  then  shake  a  little  up  with  distilled 

water,  and  note  its  reaction  with  blue  and  red  litmus  paper. 

From  a  careful  study  of  these  points,  the  following  simple  inferences  may 

safely  be  drawn ;  any  appearance  not  herein  referred  to  being  neglected  as  not 

affording  a  really  distinctive  indication. 

A.  Neutral,  no  odour,  and  leaving  no  residue  whatever.     Probably 

water. 
L.  Strongly  acid,  leaving  no  residue.     Probably  an  ordinary  volatile 

acid,  such  as  HC1,  HNO3,  HC2H,O.,,  etc. 
C   Strongly  acid,  leaving  a  residue,  fusible  by  heat  and  also  strongly 

acid.     Probably  a  non-volatile  mineral  acid,  such  as  HaPO4. 
D    Strongly  acid,  leaving  a  residue,  which   on  heating  chars,  and 
entirely    burns   away.      Probably   free    organic   acid,    such    as 
H2C4H406,  H3C6H507,  HC7H50,,  etc. 

Note  — Oxalic  and  formic  acids  do  not  char. 

E.  Neutral  or  slightly  acid,  leaving  a  residue,  which  volatilises  in 
fumes,  but  without  blackening.  Probably  an  ordinary  salt  of 
a  volatile  metal,  such  as  NH4,  Hg,  As,  Sb,  etc. 

f.  Nautral  or  slightly  acid,  leaving  a  residue  which  on  heating 
blackens  and  volatilises  in  fumes.  Probably  an  organic  salt  of 
NH4,  Hg,  or  other  volatile  metal. 

Note.  —  In  this  case  it  is  best  at  once  to  test  the  original  for  NH4  or  Hg  by  boiling 
with  KHO  and  SnCl2  respectively. 
55 


GENERAL  PRELIMINARY  EXAMINATION.  59 

G.  Neutral  or  slightly  acid,  leaving  a   residue,  which   on   heating 
changes  colour  as  follows  : — 

Yellow  while  hot,  white  on  cooling.     Probably  salt  of  Zn. 
Deep  yellow  while  hot,  yellow  on  cooling.     Probably  salt  of  Pb. 
Yellowish-brown  while  hot,  dirty  light-yellow  on  cooling.     Pro- 
bably salt  of  Sniv. 
Orange  or  red  while  hot,  dull  yellow  on  cooling.     Probably 

salt  of  Bi. 
Red  while  hot,  reddish  brown  on  cooling.     Probably  salt  of 

Fe  or  Ce. 

Permanent  brownish-black.     Certain  salts  of  Mn. 
H.  Neutral  or  slightly  acid,  leaving  a  white  residue,  which  blackens 
on  heating,  burns,  and -leaves  a  black  or  greyish  mass.     Pro- 
bably an  organic  salt  of  a  fixed  metal.     In  this  special  cast, 
proceed  as  follows: — 

Moisten  the  residue  with  a  little  water,  and  touch  it  with  reddened  litmus 
paper.  If  alkaline,  the  original  substance  was  an  organic  salt  of  K,  Na,  or 
Li,  in  which  case  proceed  by  (a).  If  not  alkaline,  proceed  by  (b\ 
(a)  Boil  the  ash  with  the  smallest  possible  quantity  of  water,  filter,  acidulate  with 
HC1  till  effervescence  ceases ;  dip  a  perfectly  clean  platinum  wire  in  the  solu- 
tion and  try  the  flame  test.  If  crimson,  Li.  Bright  yellow,  Na.  Violet,  K. 
Note. — The  latter  flame  not  being  very  easily  seen  in  the  daylight,  it  is  advisable  to 
add  to  the  solution  PtCl4  and  C2H6O.  Shake  well  and  cool.  Yellow  crystal- 
line precipitate  of  potassium  platinochloride — PtCl42KCl.  When  potassium 
is  found  with  a  tartrate  it  is  always  necessary  to  test  also  with  H2S  for 
antimony  as  the  salt  might  be  tartar  emetic. 

(V)  The  ash  is  covered  with  water  and  treated  with  HC2H3O?.  If  effervescence  takes 
place,  the  original  substance  was  probably  an  organic  salt  of  Ba,  Sr,  or  Ca  ; 
and  these  metals  may  at  once  be  tested  for  in  the  acetic  acid  solution. 
Note.  —  Oxalates,  although  organic,  do  not  blacken  to  any  extent.  If  carefully 
observed,  however,  a  slight  greyish  tint,  followed  by  a  distinct  glow  running 
through  the  mass,  will  be  noticed  at  the  moment  of  decomposition.  To  make 
certain  it  is  well  to  place  a  little  of  the  original  powder  in  one  tube,  and  the 
residue,  after  ignition,  in  another  ;  cover  them  both  with  water,  and  add  a 
drop  of  acetic  acid  to  each.  If  the  residue  effervesce,  and  the  original  powder 
does  not,  strong  presumptive  evidence  is  obtained  of  the  presence  of  an 
oxalate  of  the  alkaline  or  earthy  metals. 

/.  Neutral  or  slightly  acid,  leaving  a  residue,  which  takes  fire  and 
continues  to  burn  even  after  removal  from  the  flame,  giving  off 
clouds  of  white  fumes  and  leaving  a  fixed  white  or  pinkish 
residue.      Probably  a  hypophosphite ;    which  fact  should   be 
noted  as  an  aid  to  future  information  as  to  acid  radicals. 
K.  Strongly  alkaline,  leaving  a  fixed  white  residue,  also  alkaline. 
A  hydrate,  carbonate,  bicarbonate,  phosphate,  arseniate,  borate, 
sulphite,  or  sulphide  of  a  fixed  alkaline  metal,  or  a  hydrate  or 
oxide  of  Ba,  Sr,  or  Ca.     In  this  case  proceed  as  follows : — 
Acidulate  a  portion  of  the  original  solution  with  HC1. 

(a)  If  it  effervesces  without  odour,  and  is  therefore  a  carbonate  or  bicarbonate,  test 
at  once  by  the  flame  for  K,  Li,  Na,  and  also  another  portion  of  the  original 
solution  with  HgCl2.  If  red,  a  carbonate  :  if  not,  a  bicarbonate. 
(£)  Effervesces  with  odour  of  II2S.  In  this  case  it  is  a  sulphide ;  and  if  a  deposit 
of  S  also  takes  place,  a  polysulphide.  Add  to  a  fresh  portion  of  the  original 
solution  excess  of  HC1,  boil  till  H2S  is  expelled,  filter,  if  necessary,  and  test 
the  solution  for  all  metals  of  fourth  and  fifth  groups. 

(c)  Effervesces  with  odour  of  HCN.     Probably  an  alkal  ne  cyanide,  such  as  KCN. 

(d)  Effervescence  with  odour  of  SO,,,  an  alkaline  sulphite. 

(e)  It  does  not  effervesce.     In  this  case  add  to  a  fresh  portion   of  the   original 

solution,  AgNO3.  If  a  brownish-black  precipitate  be  formed,  it  is  a  soluKe 
hydrate.  A  portion  of  the  original  solution  should  be  neutralised  with  HC1, 
and  then  examined  for  all  metals  of  fourth  and  fifth  groups. 

Note. — If  AgNO3  with  original  solution  gives  a  yellow,  a  white,  or  k  brick-red 
precipitate,  the  presence  of  a  phosphate,  borate,  or  arseniate  of  K  or  Na  may 


6o 


QUALITATIVE  ANALYSIS. 


be  suspected.  In  the  case  of  a  complex  solution  in  which  a  salt  of  some 
other  metal  is  given  dissolved  in  excess  of  an  alkali,  an  intimation  of  the  fact 
will  be  obtained  on  cautiously  adding  the  HC1,  as,  at  the  moment  of  neu- 
tralisation, the  dissolved  substance  appears  as  a  precipitate  before  again  dissolv- 
ing in  the  excess  of  HCl.  Basic  plumbic  acetate  has  an  alkaline  reaction. 

Step  2.    Dip  a  clean  platinum  wire  in  the  solution,  or,  if  a  solid,  moisten  the 
wire  with  HCl,  dip  it  in  the  powdered  substance,  and  heat  in  the  inner 
Bunsen  or  blowpipe  flame.     The  outer  flame  is  coloured  as  under  : — 
Violet         .         .         .     Potassium. 
Golden-yellow    .         .     Sodium. 
Yellowish-green .         .     Barium. 
Crimson     .         .         .     Strontium  or  Lithium. 
Orange-red          .         .     Calcium. 
Green         .         .         .     Copper  or  Boracic  acid. 
Blue  ....     Lead,  Arsenic,  Bismuth  ; 

also  Copper  as  chloride. 

Step  3.     Heat  a  little  of  the  solid  substance  (or  the  residue  left  on  evapora- 
tion if  in  solution)  on  charcoal  before  the  blowpipe. 

Ordinary  alkaline  salts  fuse  and  sink  into  the  charcoal ;  some  decre- 
pitating (example  Nad,  etc.).  others  deflagrating  (as  KNO3,  KC1O3, 
etc.),  but  no  sufficiently  characteristic  indications  are  usually  obtained, 
except  in  one  of  the  following  cases  : — 

A.  A  white  luminous  residue  is  left.     Moisten  it  when  cold  with  a 

drop  or  two  of  cobaltous  nitrate,  and  again  apply  the  blowpipe, 

observing  any  change  of  colour  as  follows  : — 

The  residue  becomes  blue,  indicating  Al,  Silicates,  Phosphates, 

or  Borates. 
green,        „         Zn. 
,,  „  „        pink  or  flesh-coloured,  indicating  Mg. 

B.  A  coloured  residue  is  left.     Prepare  a  borax  bead,  and  heat  a  little 

of  the  substance  in  it,  both  in  the  reducing  and  oxidising  flame, 
and  note  any  colours  corresponding  with  the  following  list : — 


METAL. 

IN  OXIDISING  FLAME.                           IN  REDUCING  FLAME. 

I 

Cu 
Co 

Green  (hot).     Blue  (cold). 
Blue. 

Red  (cold). 
Blue. 

Cr 

Green. 

Green. 

Fe 
Mn 

Ni 

Red  (hot).     Yellowish  (cold). 
Amethyst. 
Reddish-brown  (hot).     Yellow  (cold). 

Bottle-green. 
Colourless. 
Same  as  oxidising  flame. 

C.  A  metallic  residue  is  left,  with  or  without  incrustation  surrounding 
it.  Mix  a  little  of  the  substance  with  KCN  and  Na2COs,  and 
expose  on  charcoal  to  the  reducing  flame. 

(a)  Metallic  globules  are  produced  without  any  surrounding  incrusta- 

tion of  oxide.  This  occurs  with  Ag,  Au,  Cu,  Fe,  Co,  and  Ni, 
all  easily  recognisable. 

(b)  Metallic  globules  are  produced  with  a  surrounding  incrustation  of 

oxide.  This  occurs  with  Sn,  Bi,  Pb,  and  Sb  ;  the  incrustation 
having  the  characteristic  colours  already  described  in  Case  I., 
Step  i,  G. 

Nole.  —  Sb  often  forms  a  white  and  distinctly  crystalline  crust. 
(f)  The  metal  volatilises,  and  only  leaves  an  incrustation  of   oxide. 
This  occurs  with  As  (odour  of  garlic,  and  white  incrustation), 
Zn  (yellow  [hot],  white  [cold]),  and  Cd  (reddish-brown). 


DETECTION  OF  METALS  IN  SALTS.  61 

§  II.  DETECTION  OF  THE  METAL  PRESENT  IN  ANY  SIMPLE  SALT. 

Step  1.     Preparation  of  the   solution  for  analysis  for  the  metal,  if  the 
substance  be  not  already  dissolved. 

1.  Take  a  minute  portion  of  the  substance  and  boil  it  with  water  in 

a  test-tube;  should  it  dissolve,  then  take  a  large  portion  and 
dissolve  for  testing. 

2.  Should  the  salt  prove  insoluble,  take  another  small  portion  and  heat 

with  HC1,  and  add  a  little  water  and  again  heat.  If  it  now 
dissolves,  prepare  a  larger  quantity  of  the  solution  for  use  in 
the  same  manner. 

3.  Should  it  resist  HC1,   try  another  small   portion   with   HN03   by 

heating  and  then  adding  water.  If  this  dissolves  it,  make  up 
a  larger  quantity  of  a  similar  solution  for  testing. 

4.  Should  HNO3  also  fail,  try  another  small  portion  with  two  parts  HC1 

and  one  part  HN03,  warming  and  diluting  as  before;  and  if  it  suc- 
ceeds, make  up  a  larger  amount  of  solution  in  the  same  manner. 

5.  If  all  acids  fail,  then  take  another  portion  of  the  substance,  mix  it 

with  several  times  its  bulk  of  a  perfectly  dry  mixture  of  sodium 
and  potassium  carbonates  (prepared  by  heating  Rochelle  salt  in 
an  open  crucible  until  the  residue  thoroughly  ceases  to  evolve 
any  gases,  then  extracting  with  distilled  water,  filtering,  evapo- 
rating to  dryness,  heating  the  residue  to  redness,  and  preserving 
for  use  in  a  stoppered  bottle.  This  reagent  will  hereafter  be 
shortly  described  as  fusion  mixture).  Place  the  whole  in  a 
platinum  crucible,  and  fuse  at  a  bfright-red  heat;  when  cold, 
boil  with  water  and  save  the  solution  thus  obtained  for  acid 
radicals.  The  insoluble  matter  is  then  to  be  drenched  with 
strong  HC1,  slightly  diluted  and  boiled,  and  the  solution  used 
for  testing  for  the  metal.  Any  insoluble  white  gritty  matter 
still  remaining  is  put  down  as  silica. 

Step  2.    Detection  of  the  metal. 

The  processes  to  be  applied  vary  according  to  the  limitation  of  the  possible 
substances  under  examination,  and  the  following  tables  are  to  be  used  accord- 
ingly, using  the  solution  obtained  in  Step  i.  Remember  that  even  when  we 
have  apparently  found  out  the  metal  by  the  table,  we  should  always  proceed  to 
perfect  confirmation  by  applying  (to  fresh  portions  of  the  solution  each  time)  all 
the  tests  for  the  metal  given  in  Chapter  II.  Unless  otherwise  directed,  all 
confirmations  referred  to  in  the  tables  are  intended  to  be  tried  upon  fresh 
portions  of  the  original  solution.  For  brevity  the  said  solution  is  in  the 
tables  indicated  by  a  capital  0  in  thick  type,  and  the  word  precipitate  is 
contracted  to  ppt.  In  simple  salts  we  go  through  the  groups  until  we  get  a 
result,  and  as  soon  as  we  do  we  stop  and  go  no  farther  with  the  groups,  but 
simply  confirm  the  result  obtained  by  special  tests. 

The  following  brief  instructions  may  aid  the  student  to  find  readily  the  pages  required  foi 
the  full  analysis  of  a  simple  salt  : — 

1.  Find  whether  soluble  in  H2O  or  in  acids,  or  neither. 

(  acid  =  free  acid  or  acid  salt. 

2.  Take  the  reaction  <  alkaline  =  complete  the  analysis  by  "  K,"  p.  59. 

(  neutral. 

3.  Heat  *,  „.«  tube  {<£  tt^SS?  See  -  H,"  p.  59- 

4.  Find  the  metal  by  p.  64. 

(  solubility  table,  p.  82. 

5.  Find  the  acid  radical  by   \      If  K,  Na,^ tables  pp.  76  to  80,  if  inorganic. 

(  Li,  or  NHJ      ,,     p.  80  if  organic. 

6.  Name  the  salt  and  write  its  chemical  formula. 


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DETECTION  OF  UNKNOWN  SALTS.  05 

in.  DETECTION  OF  THE  METALS  IN  COMPLEX  MIXTURES  OF 
TWO  OR  MORE  SALTS. 

Step  I.  Preparation  of  the  solution  for  analysis  in  cases  where  the 
substance  for  analysis  is  not  given  in  solution. 

Note. — By  carefully  applying  this  step  and  intelligently  judging  the  results,  we  can 
often  reduce  a  separation  of  two  salts  to  the  performance  of  two  separate 
simple  analyses,  and  so  save  much  time  and  trouble. 

1.  Boil  some  of  the  powdered  substance  with  distilled  water,  and  filter 

off  from  any  insoluble  matter. 

Evaporate  a  drop  or  two  of  the  filtrate  to  dryness,  at  a  gentle  heat,  on  a 
slip  of  clean  platinum  foil,  and  if  any  residue  be  left,  then  save  the  balance 
of  the  filtrate  for  analysis  as  representing  the  portion  of  the  original  (if  any) 
that  is  soluble  in  water. 

2.  If  anything  remains  insoluble  in  water,  then  wash  it  on  the  filter 

with  boiling  water  until  a  drop  of  the  washings  leaves  no  marked 
residue  on  evaporation.  Rinse  the  insoluble  portion  off  the  paper 
into  a  tube,  and  add  hydrochloric  acid  drop  by  drop  (noting 
carefully  any  effervescence  or  odour  as  indicating  the  presence 
of  certain  acid  radicals,  such  as  carbonates,  sulphides,  sulphites, 
cyanides,  etc.),  and  warm. 

If  it  now  all  dissolves,  save  the  fluid  for  anajysis.  If  not,  then  separate 
the  insoluble  part,  test  the  filtrate  by  evaporation  of  a  drop  or  two,  to  see 
whether  anything  has  dissolved,  and  if  so,  save  the  fluid  for  analysis  as  repre- 
senting the  metals  present  in  the  form  of  salts  insoluble  in  water,  but  soluble 
in  HC1. 

Note. — This  division  of  any  mixture  into  salts  soluble  and  insoluble  in  water  gives 
the  greatest  assistance  in  the  subsequent  testing  for  the  acid  radicals.  For 
example,  if  a  metal  of  the  5th  group  be  found  in  the  portion  soluble  in  water? 
then  any  acid  radical  almost  may  be  present ;  while  if  a  metal  of  one  of  the 
other  groups  be  found,  then  generally  speaking  only  a  nitrate,  sulphate, 
chloride,  or  acetate  need  be  first  searched  for.  If,  on  the  other  hand,  the 
substance  resists  the  action  of  water  and  only  goes  into  solution  with  HC1, 
then  as  a  rule  no  metal  of  the  ^th  group  is  present,  and  we  might  consider  that 
we  were  probably  dealing  with  a  carbonate,  oxide,  phosphate,  arseniate, 
oxalate,  sulphide,  sulphite,  cyanide,  ferro-  or  ferri-cyanide,  or  borate  of  a 
metal,  not  in  the  5th  group.  Certain  tartrates  and  citrates,  chiefly  of  the  4th 
group,  would  also  come  in  this  category. 

j.  If  the  substance  is  insoluble  in  both  water  and  HC1,  try  nitric  acid, 
first  alone,  and  then  with  the  addition  of  hydrochloric  acid. 

This  treatment  dissolves  certain  metals  in  the  free  state,  such  as  Ag,  Pb, 
Bi,  Hg,  and  Cu,  and  also  acts  upon  Hg2Cl2,  HgS  and  other  insoluule  sul- 
phides, and  on  Fe2O3  and  some  refractory  oxides.  Gold  and  platinum  dis- 
solve only  ii  nitre-hydrochloric  acid. 

Note.—  When   H  \TO3  has  been  used  as  a  solvent,  the  liquid  should  always  be 
evaporated  A.ith  HC1  till  all  the  HNO3  has  been  displaced,  then  allowed  to 
get  quite  cold  and  any  precipitate  filtered  out  and  treated  as  belonging  to 
the  1st  group,   vhile  the  filtrate  is  directly  treated  with  H^S. 
4.  If  anything  still   remains  insoluble,  it  must  be  fused  with  fusion 
mixture  (KNaCO3)  at  a  bright  red  heat  till  action  ceases,  and 
the  residue  so  obtained  boiled  with  water  and  filtered. 

The  filtrate  is  used  for  the  detection  of  acid  radicals  ;  while  the  insoluble 
matter  is  dissolved  (after  washing)  in  nitric  acid  and  used  for  finding  the 
metals.  The  usual  run  of  articles  requiring  this  treatment  are — sand,  clay, 
and  other  silicates,  sulphates  of  Ba,  Sr,  Ca  (latter  not  always),  and  Pb,  the 
haloid  salts  of  silver,  SnO2  and  Sb2O5. 

Step  II.  Proceed  to  apply  the  following  tables  to  the  prepared  solution 
from  Step  I. 

Note. — The  whole  of  the  first  table  for  "separation  into  groups"  must  be  gone 
through,  but  if  no  effect  be  obtained  in  Groups  I.  or  II..  a  fresh  portion  of 
the  prepared  solution  should  be  taken  for  Group  III.,  etc.,  so  saving  the 
time  required  for  evaporating  to  a  considerable  extent. 

5 


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DETECTION  OF  UNKNOWN  SALTS.  75 

§  IV.  DEIECTION  OF  THE  ACID  RADICALS. 
Division  A. — Preliminary  Examination. 

IMPORTANT  NOTE. — We  must  always  decide  what  metals  or  bases 
are  present  before  we  proceed  to  test  for  acid  radicals.  We 
must  then  note  which  bases  are  present  as  soluble  and  which 
as  insoluble  salts  (in  H2O).  Lastly,  we  must  consider  what 
acids  might  be  present  in  each  case,  and  only  test  for  such 
possible  acids,  because  nothing  leads  to  so  many  errors  as  testing 
for  acids  which  could  not  possibly  exist.  We  must  also  carefully 
note  the  information  received  in  the  former  preliminary  exami- 
nation, especially  as  regards  the  presence  of  organic  matter, 
and  remember  that,  if  the  original  substance  does  not  char  on 
heating  we  must  never  enter  into  the  testing  for  organic  acids, 
because  none  can  possibly  be  present  except  oxalate,  which  is 
provided  for  in  the  inorganic  portion  of  the  course  with  this 
very  object,  together  with  a  few  others  included  for  convenience. 
We  must  also  remember  to  note  what  happens  when  we 
dissolve  the  original  substance  in  HC1,  provided  such  a  step 
is  necessary,  and  if  any  effervescence  occurs  we  must  be  sure 
to  smell  the  gas  given  off,  because  we  may  then  at  once  detect 
the  following : — 

*Carbonate       .         .  effervescence  without  odour,  and  the  evolved  gas 

poured  into  lime-water  renders  it  milky. 

*Sulphide         .         .  odour  of  H.  S  (with  deposit  of  S  polysulphide). 
*Sulphite         .         .        „          SO2  (         „          „         hyposulphite). 
*Cyanide         .         .        „          HCN. 
Peroxide          .         .        „          chlorine. 
Fe,  Zn,  or  Sn  (as  metals) — Hydrogen  evolved ;  without  odour. 

We  must  also  remember  that  organic  bodies,  such  as  alkaloids  or 
sugar,  other  than  organic  salts,  might  be  contained  in  a  mixture 
which  would  cause  charring  on  heating,  and  so  lead  us  to  test 
for  what  was  not  there.  It  will  be  useful  at  this  point  to  see 
how  we  can  guard  against  two  of  the  more  commonly  occurring 
of  such  cases. 

(1)  Sugar.     This  will  cause   the  soluble  portion   to  be  syrupy,  and 

when  warmed  with  dilute  H2SO4  it  will  rapidly  darken,  whereas 
organic  salts,  as  a  rule,  require  fairly  strong  H2SO4  to  char 
them.  The  solution  will  have  a  sweet  taste,  and  after  boiling 
with  a  drop  or  two  of  very  dilute  H2SO4  it  will  reduce  Fehling's 
solution. 

(2)  Alkaloids  (nitrogenous  organic  bases).     These  will  cause  an  odour 

like  burning  hair  on  heating  to  redness.  The  soluble  portion  of 
the  mixture  carefully  treated  with  very  dilute  NH4HO  will 
usually  give  a  cloud  (which  may  or  may  not  dissolve  in  excess), 
and  then  the  same  liquid  shaken  up  with  chloroform,  and  the 
chloroform  evaporated  at  a  gentle  heat,  will  leave  the  alkaloid 
as  a  residue.  If  no  residue  be  thus  obtained,  then  no  alkaloid 
can  be  present  except  morphia,  and  this  latter  would  never  be 
put  in  a  mixture  unless  specially  intended  for  toxicological  inves- 

*  In  soluble  salts  these  effects  will  come  on  adding  HC1  in  Group  I. 


QUALITATIVE  ANALYSIS. 


tigation,  because  its  detection  requires  altogether  special  work, 
which  will  be  afterwards  detailed. 

Having  well  considered  all  this,  we  now  proceed  to  the  actual 
work,  carefully  remembering  that  all  the  indications  are  merely 
preliminary,  and  that  we  are  not  to  take  notice  unless  we  really 
get  a  distinct  result.  If  we  really  do  get  one,  then  it  may  save 
us  going  so  far  through  our  actual  acid  course,  but  if  we  are  not 
certain,  then  it  is  no  use  attempting  to  persuade  ourselves  and 
wasting  time,  but  we  should  just  note  the  probability  and  then 
at  once  pass  on  to  confirm  by  the  actual  course  hereafter 
detailed. 

No  attempt  is  made  to  describe  odours,  because  the  student 
should  simply  put  himself  through  a  course  of  training  for  this 
preliminary  examination  on  known  salts,  and  learn  to  recognise 
all  the  odours,  etc.  This  is  a  most  important  study,  and  should 
be  carefully  stuck  to,  until  the  nose  and  eyes  have  been  quite 
trained  to  recognise  the  individual  effects  to  be  expected  from 
each  acid. 

Step  I.  Put  a  portion  of  the  original  solution  in  a  tube,  or  if  it  be  a 
solid  cover  it  with  some  water,  just  acidulate  with  dilute  H2S04, 
and  look  for  any  effervescence  or  odour,  then  boil  and  smell. 
The  following  radicals  may  be  thus  recognised  : — 

Effervescence  without  odour  .         .  Carbonate. 

^Sulphide. 

Effervescence  with  characteristic  odours  .       )  Sulphite. 

)  Cyanide. 

(Hypochlorite. 
Red  fumes Nitrite. 

Step  II.  Add  another  drop  of  H2S04,  and  again  warm. 

Odour  of  vinegar Acetate. 

„       „     SO2    with  deposit  of  S  .         .         Hyposulphite. 
„       „     HCN    „         ,,         „  .         Sulphocyanate. 

„       „     HCN    „    crystalline  deposit,      f  Ferro-  or 

often  bluish  (  J*erri-cyanide. 

„       „     Valerian  or  sharp  odour  1  v^rianate,     Ben- 

(     zoate,  buccmate. 
„       „     Carbolic  acid         .         .  Carbolate. 

Note.— The  effects  of  Step  II.  will  often  come  perfectly  in  Step  I.,  ana 
than  Step  II.  may  be  considered  as  part  of  Step  I. 

Step  in.  Put  a  little  of  the  original  solid  (or  the  residue  left  on  evapo- 
ration if  the  original  was  a  liquid)  into  a  dry  tube,  cover  it 
with  strong  H£S04,  and  warm,  but  not  sufficiently  to  cause  the 
H2SO4  itself  to  fume.  (See  note,  important  to  prevent  accidents.) 

Thus  we  get  :— 

Chloride.  /Iodide 

NitmtP  Change  of  colour  (f°    Jf- 


White  fumes 
(characteristic  of) 


Nitrate.  "   lodate 

Flimrirlff  and  coloured 

B±at  fume,  (char-    }*™£ 

Succinate.  actenstic  of) 
Sulpho-carbolate. 


DETECTION  OF  UNKNOWN  SALTS.  77 


Effervescence  on  warming  only, 
which  persists  after  withdraw- 
ing from  flame,  but  with  no 
darkening  in  colour  and  no 
odour. 


Effervescence  on  warming,  but 
the  liquid  darkens  in  colour  * 
to  a  greater  or  less  extent. 


Formates — give  off  CO  only,  and  con- 
sequently the  gas  does  not 
affect  lime-water. 

Oxalates—g\\e  both  CO  and  CO2,  and 
the  gas  therefore  renders 
lime-water  milky. 

Tartrates — rapid   charring    and    smell 

of  burnt  sugar. 
Lactates — not    so   dark,   and    peculiar 

odour. 
Citrates — slow  darkening  and  peculiar 

sharp  odour. 
Oleates — char    and     give     odour     of 

acrolein. 


Meconate. 

Darkening  in  colour  without  any  I   , 

very  marked  effervescence.      1  pyrogajlate. 

{  Salicylate  (very  slow  darkening). 

No  fumes — gelatinous  deposit  (or  flaky) — Silicate. 
„       „     — scaly   crystals   with    pearly   lustre — Borate    (best    seen    on 

cooling). 

No  change  takes  place  at  all  with — Sulphate,  phosphate,  and  arseniate. 
Chromates  turn  orange  and  then  green — Bichromates  turn  green  straight 
off. 

NOTE,  IMPORTANT. — On  adding  strong  sulphuric  acid  to  any  solid,  one  drop 
only  should  be  first  carefully  applied,  because  chlorates,  iodates,  etc.,  are  apt 
to  explode  on  the  first  touch  of  the  acid. 

If  we  get  a  decided  indication  of  the  presence  of  any  acid  radical  as 
above,  we  may  at  once  apply  confirmatory  tests  for  the  radical  found  to 
onr  original  substance,  and  so  save  going  through  the  course,  especially 
if  the  substance  be  soluble  in  water ;  but  if  insoluble,  a  solution  must 
always  be  specially  prepared  for  acid  testing. 

Division  B. — Preparation  of  a  Solution  for  Testing  for  Acid  Radical, 

The  success  of  the  course  for  the  detection  of  acids  depends  in  the  highest 
degree  upon  the  care  with  which  the  solution  is  first  prepared.  It  may  be 
taken  as  a  general  rule  that  no  testing  for  acids  is  reliable  unless  they  are 
present  in  the  form  of  salts  of  alkaline  metals.  It  is  therefore  necessary  to 
transform  our  acids  into  such  salts  ;  and,  to  do  this  successfully,  the  following 
rules  must  be  closely  adhered  to  : — 

I.  If  the  original  is  soluble  in  water,  and  absolutely  neutral  to  test- 
paper,  you  may  venture  as  a  rule  to  use  it  as  it  is,  and  this  will 
also  apply,  if  it  be  alkaline,  to  test-paper. 

II.  If  the  original  be  soluble  in  water,  but  in  the  least  acid,  we  must 
drop  in  NaHO  till  it  is  rendered  just  alkaline,  boil,  and,  if  any 
precipitate  should  form,  filter  and  use  the  filtrate  for  the  acid 
course. 

III.  The  portion  insoluble  in  water  (or  the  whole  of  the  original  if  all 
insoluble)  must  be  boiled  with  a  little  NaHO,  then  diluted, 
filtered,  and  the  filtrate  orrly  used  for  the  acid  course. 


QUALITATIVE  ANALYSIS. 


tfotc.—lt  Al,  Zn,  Sb,Sn,  Cr,  Pb,  or  any  metal  whose  hydrate  is  soluble 
in  excess  of  NaHO  has  been  found,  then  we  must  use  a  solution 
of  Na2CO3  instead  of  NaHO  in  both  Cases  II.  and  III. 

We"  must  also  take  care  to  prepare  plenty  of  our  solution, 
because  if  the  full  acid  course  has  to  be  gone  through,  we  shall 
require  possibly  to  employ  eight  to  ten  different  portions  before 
we  have  finished. 

This  course  now  about  to  be  explained  is  so  devised  that  by  working  upon 
the  prepared  solution,  in  the  presence  successively  of  HC1,  HN(X,  HQjH/),, 
H2SO4  and  absolute  neutrality,  we  can  insure  the  precipitation  in  each  stage 
of  certain  given  acid  radicals  only  by  reagents,  which,  if  used  without  such 
precautions,  wrould  precipitate  many  more  than  they  do  when  so  employed. 

Division  C.— Course  for  the  Detection  of  Inorganic  Acids  together  with 
a  few  Organic  included  for  certain  reasons, 

Step  I.  Acidulate  a  portion  of  the  prepared  solution  with  HC1,  and 
then  to  successive  portions  thereof  apply  the  following  tests  : — 


REAGENT. 


EFFECT. 


ACID  PRESENT. 


(a)  BaCl2 


FeCl« 


(c)  FeSO, 


(d)  Turmeric  paper  . 


(White  ppt.   insoluble  in| 
1     boiling  HNO3    .     .    j" 

'Dark  blue  ppt 

Blood  red  colour  dis- 
charged by  HgCl2  . 

Blood  red  colour  not  dis- 
charged by  HgCl2  .  . 


Dark  blue 


Dip  in  and  dry  over  the 
gas    when    the    paper 
turns    pink,    changed/ 
to  green  by  KHO.  .    j 


Sulphate. 

Ferrocyanide. 
Sulphocyanate. 
Meconate. 
Ferricyanide. 

B  orate. 


Step  II.  Acidulate  a  portion  of  the  prepared  solution  with  HNO  , 
add  excess  of  AgNO  ,  warm  and  shake,  disregarding  any  precipi- 
tate that  is  not  white  or  yellow  and  distinctly  curdy.  Thus  we 
get  the  following : — 

(a)  Cyanide — Curdy  white  ;  soluble  in  very  dilute  NH4HO,  and  also 
in  boiling  HNOs. 

(£)  Chloride— Curdy  white  :  soluble  in  very  dilute  NH4HO,  but  in- 
soluble in  boiling  IIXOs. 

to  Bromide— Curdy  dirty  white;  slowly  soluble  in  fairly  strong 
XHjIK),  but  not  in  very  dilute;  insoluble  in  HNO3. 

(d)  Iodide— Curdy  pale  yellow;  insoluble  even  in  strong  NH.HO  and 
also  in  I  IN' 

Note.—  Many  other  acids,  such  as  ferrocyanidc,  oxalate,  eliminate,  etc.,  are  apt  to  come 
down  with  AgXO3  in  presence  even  of  HNO3,  but  the  precipitates  are  (if 
white)  uotairdy,  or  they  are  coloured  red  and  so  will  be  disregarded  ;  and  we 
therefore  deal  only  with  the  four  acids  mentioned  giving  curdy  precipitates. 


DETECTION  OF  UNKNOWN  SALTS. 


79 


To  distinguish  between  these  four  acids  we— 

(1)  Filter  out  the  precipitate  with  AgNO3,  wash  it,  and  then  percolate  it 

several  times  with  very  dilute  NH4HO  (i  in  20),  when  AgCl  and 
AgCN  will  dissolve,  and  can  be  reprecipitated  from  the  filtrate  by 
HNOs,  while  any  AgBr  or  Agl  will  be  left  on  the  filter. 

Note. — It  is  very  important  to  have  the  dilute  NH4HO  exactly  I  in  20,  because, 
if  stronger,  then  AgBr  will  also  dissolve,  and  in  any  case  a  mere  cloud  on 
adding  the  HNO$  is  to  b^  disregarded,  because  if  AgCl  or  AgCN  be  really 
present,  they  will  reprecipitate  in  distinct  curds,  on  adding  HNO3,  warming 
and  shaking. 

(2)  If  by  (i)  evidence  of  the  presence  of  Cl  or  CN  be  obtained,  then 

test  a  portion  of  the  original  prepared  solution  for  CN  by 
Scheele's  test,  and  if  not  present  then  the  precipitate  was  all  due 
to  Cl.  If  CN  be  found,  then  another  precipitate  must  be 
obtained  by  excess  of  AgNO3,  filtered,  washed,  drained,  and 
transferred  to  a  tube  with  strong  HNO3  and  boiled,  when  any 
AgCl  will  remain  insoluble. 

Note. — As  HCN  is  so  easily  smelt  in  the  preliminary  examination,  we  should  always 
know  before  we  begin  the  group  whether  it  is  there,  and  then  if  it  be  present 
the  boiling  with  HNO3  will  be  required,  but  if  not,  then  we  put  it  down  at 
once  as  chloride  if  the  NH4HO  dissolves  anything. 

(3)  If,  after  treating  with  NH4HO  (i  in  20),  any  residue  be  left  on  the 

filter,  leading  to  the  idea  that  AgBr  or  Agl  may  be  present,  we 
proceed  as  follows  :  To  a  small  portion  of  our  prepared  solution 
a  drop  of  mucilage  of  starch  is  added,  and  then  one  or  two  drops 
of  chlorine  water.  If  iodide  be  present  we  shall  get  a  blue. 
Now  we  go  on  adding  fresh  chlorine  water  till  all  the  blue 
has  been  bleached,  and  if  the  whole  is  now  perfectly  white  only 
iodide  is  present ;  but  if  it  remain  at  all  yellow,  then  we  add 
some  chloroform  and  shake  up,  when  an  orange  colour  in  the 
chloroform  will  indicate  bromide.  This  depends  on  the  fact 
that  free  iodine  combines  with  chlorine  more  readily  than  with 
bromine. 

Step  III.  Acidulate  a  portion  of  the  prepared  solution  with  acetic  acid, 
bring  it  to  the  boil,  and  then  test  successive  portions  while 
boiling  as  follows  : — 


REAGENT. 

EFFECT. 

ACID  PRESENT. 

(a)  CaCl2  .... 
(It)  Fe2Cl6(«0/irn 

White  ppt.  soluble  in  HC1  . 
White  ppt  

Oxalate. 
j  Phosphate  or 

excess)  )  ' 
M  Pb(C2H  A)2  -  - 

Yellow  ppt  

(     Arseniate. 
Cbromate. 

To  distinguish  between  phosphate  and  arseniate  exactly 
neutralise  a  portion  of  the  prepared  solution  with  dilute  HNO.J 
and  add  AgN03. 

Yellow  precipitate  soluble  in  NH4HO  ==  Phosphate 
Red  =  Arseniate 


QUALITATIVE  ANALYSIS. 


Step  IV.  Just  acidulate  a  portion  of  the  prepared  solution  with  dilute 
H,S04,  then  add  a  strong  and  fresh  solution  of  FeS04,  and  run 
some  strong  H2S04  down  the  side  of  the  tube  so  that  it  collects 
at  the  bottom.  A  dark  ring  where  the  liquids  meet  proves 
Nitrate. 

Kate.—  If  ro//V&has  been  previously  found,  this  test  fails  to  be  conclusive,  and  in  such 
case  we  must  take  advantage  of  the  power  of  nascent  hydrogen  to  reduce 
nitrates  to  ammonia.  If  no  salt  of  NH4  has  been  found  in  metal  testing,  we 
add  to  some  of  the  prepared  solution  a  fragment  of  zinc  and  sufficient  HC1 
to  cause  a  brisk  effervescence.  After  ten  minutes  we  add  excess  of  KHO 
and  boil,  when  an  odour  of  NH3  proves  Nitrate.  If  NH4  salts  be  present 
we  add  a  little  KHO  to  the  prepared  solution,  evaporate  to  dryness,  heat 
the  residue  till  no  more  fumes  are  evolved,  and  then  dissolve  in  water  and 
apply  the  zinc,  etc.,  as  above  described. 

Extra  Step.  lodates  being  very  difficult  to  detect  in  the  preliminary, 
it  is  well  to  test  for  them  specially  (if  they  can  possibly  be 
present)  by  adding  to  the  .prepared  solution  KI  and  starch 

,  paste,  and  acidulating  with  tartaric  acid.  This  is  not  reliable 

in  presence  of  nitrites. 


Division  D. — Course  for  the  Detection  of  Organic  Acids. 

(Only  to  be  entered  upon  in  the  event  of  the  original  substance  being  proved  to 
contain  organic  matter  by  charring  on  heating  in  the  preliminary  examination.} 

The  solution  to  be  used  is  that  prepared  for  acid  testing,  as  already  described. 

Step  I.  Place  a  minute  fragment  of  litmus  paper  in  a  little  of  the  pre- 
pared solution  and  add  acetic  acid  drop  by  drop  with  agitation 
until  the  paper /w/  turns  red,  then  take  out  the  paper  and  add 
AgN03in  excess,  lastly  add  a  drop  or  two  of  very  dilute  NH4HO 
till  the  precipitate/*^1/1  commences  to  redissolve.  Now  warm  the 
tube  in  the  Bunsen  flame,  when  a  reduction  to  metallic  silver, 
forming  a  mirror  on  the  tube  =  Tartrate. 

Note. — The  tube  used  must  first  be  rendered  chemically  clean  by  boiling  in  it 
successively  some  dilute  HNO3  and  then  some  dilute  NaHO,  and  rinsing 
with  distilled  water.  Formates  produce  the  same  effect,  but  do  not  char  on 
heating. 

Step  II.  Place  a  minute  fragment  of  test-paper  into  a  portion  of  the 
prepared  solution,  and  drop  in  dilute  HC1  till  it  just  turns  red, 
then  dilute  NH4HO  till  \\.just  turns  blue  again,  cool  thoroughly, 
add  some  CaCl.,  and  shake  well.  If  a  precipitate  forms  (oxalate, 
tartrate,  etc.),  add  excess  of  CaCl.,,  shake,  and  let  it  stand  in 
cold  water  for  ten  minutes  and  filter.  Now  add  to  the  filtrate 
a  little  more  NH4HO  and  boil  gently  for  some  time,  when  a 
white  precipitate  =  Citrate. 

Kote. — If  CaClj  gives  nothing  in  the  cold,  of  course  we  simply  warm  for  the  citrate 
straight  off.  As  oxalate,  tartrate,  etc.,  have  all  been  previously  tested  for,  we 
shall  know,  before  commencing  to  test  for  a  citrate,  whether  we  need  to 
separate  them  in  the  cold  or  simply  to  add  the  NH4HO  and  CaCl2  and  boil 
straight  away. 

The  addition  of  rectified  spirit  to  the  solution  in  which  boiling  has  failed 
to  indicate  citrate  will  bring  down  a  Malatc  on  cooling,  but  unless  specially 
•  ctcd  this  reaction  is  not  a  very  certain  one. 

Step  III.  Place  a  fragment  of  test-paper  into  a  portion  of  the  prepared 
solution,  and  if  alkaline,  make  it  exactly  neutral  by  carefully 


DETECTION  OF  UNKNOWN  SALTS. 


dropping  in  dilute   HC1.     Then  apply  the  following  tests  to 
portions  of  the  neutralised  liquid  :  — 

(a)  Prepare  some  neutral  ferric  chloride,  by  adding  very  dilute  NH4HO 
to  a  solution  of  Fe2Cl6  until  a  permanent  cloud  just  forms,  and 
filtering. 

Now  add  some  of  this  reagent,  and  observe  effect  as  follows:  — 
Acetate  (Carbolate 

(i)  Red  colour    .  Sulphocyanate  (2)  Purple  colour     1  Sulphocarbolate 


(3)  Blue-black  «  Pi"kish 


Notes. 

(1)  Acetate,  red,  is  instantly  discharged  by  a  drop  of  HC1  ;  pyrogallate  is  turned 

black  by  excess  of  KHO  and  exposure  to  air.  Sulphocyanate  and  meconate 
have  been  already  proved  in  the  inorganic  acid  course,  but  distinguished  by 
action  of  HgCl2  if  desired. 

(2)  Acidulate  a  portion  of  prepared  solution  with  HC1  and  shake  up  with  ether. 

Remove  the  ether  by  a  pipette  and  evaporate  it  on  a  watch-glass  at  a  very 
gentle  heat.  Carbolic  acid  is  left,  an  oily  liquid  readily  recognised,  while 
salicylic  acid  is  left  in  characteristic  crystals,  as  giving  a  beautiful  violet 
with  Fe.;Cl6.  (Also  see  page  57  for  another  separation.)  Sulphocarbolic 
acid  gives  no  immediate  precipitate  with  BaCl2,  but  on  evaporating  with  a 
little  Na2CO3and  KNO3,  and  fusing,  then  the  residue  dissolved  in  H2O  shows 
a  sulphate  with  Bad,. 

(3)  With  excess  of  KHO  a  solution  of  gallic  acid  rapidly  becomes  dark  on  exposure 

to  the  air,  while  tannic  acid  gives  a  flocculent  liquid  not  so  rapidly  changing. 
Tannic  acid  also  precipitates  solution  of  gelatine,  and  gallic  does  not. 

(4)  Take  a  good  quantity  of  the  neutralised  and  prepared  solution,  add  excess  of 

Fe2Cl6,  filter  out  the  precipitate  and  wash  it.  Now  percolate  it  with  some 
dilute  NH4HO,  evaporate  the  liquid  so  obtained  to  a  low  bulk,  cool 
thoroughly,  and  acidulate  with  HC1.  Benzoic  aoid  will  separate  in  silky 
crystals,  and  succinic  acid  will  not. 

Step  IV.  If  oleic,  lactic,  or  sulphovinic  (ethyl-sulphuric)  acids  be 
suspected,  specially  test  for  them  as  follows:  — 

Oleic  acid  will  have  shown  its  presence  by  always  floating  to 
the  surface  as  an  oily  liquid  whenever  the  prepared  solution  is 
acidulated  with  any  acid.  To  confirm  and  distinguish  it  from 
the  other  fatty  acids  (stearic,  etc.),  take  some  of  the  prepared 
solution  and  acidulate  with  HC1,  warm,  and  set  aside  till  the 
oily  layer  floats  up.  Now  remove  the  liquid  beneath,  as  far  as 
possible,  with  a  pipette,  add  some  water,  boil,  and  drop  in  small 
fragments  of  K^COg,  until  the  oily  layer  is  saponified  and 
dissolves.  Now  put  in  a  piece  of  test-paper  and  carefully  add 
acetic  acid  to  exact  neutrality,  then  cool  and  precipitate  with 
excess  of  Pb(C2H3O2)2.  Filter  out  the  oleate  of  lead,  wash  it 
with  boiling  water,  let  it  thoroughly  drain,  and  then  prove  that 
it  is  soluble  in  ether  (stearate  and  palmitate  of  lead  are 
insoluble). 

Lactic  acid.  Acidulate  the  prepared  solution  with  HC1  and  shake  up 
with  ether.  Pipette  off  the  ether  into  a  porcelain  capsule  and 
let  it  evaporate  at  a  gentle  heat,  when  the  acid  will  be  left  and 
may  be  recognised  as  follows  :  (a)  A  portion  heated  burns  at 
first  with  a  blue  flame,  and  then  the  flame  becomes  luminous 
as  the  temperature  rises.  (^)  Another  portion  warmed  with 
K2Mni;O8  gives  the  odour  of  aldehyd. 

Sulphovinates  do  not  precipitate  BaCl2  in  the  cold,  but,  on  boiling, 
give  a  precipitate  of  BaSO4  and  an  odour  of  spirit. 

6 


QUALITATIVE  ANALYSIS. 


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DETECTION  OF  UNKNOWN  SALTS. 


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CHAPTER    V. 

QUALITATIVE  DETECTION  OF  ALKALOIDS  AND  OTHER 
ORGANIC  BODIES  USED  IN  MEDICINE,  TOGETHER 
WITH  THE  TESTING  OF  "SCALE  PREPARATIONS" 
AND  A  GENERAL  SKETCH  OF  TOXICOLOGICAL  PRO- 
CEDURE. 


DIVISION  A.     COURSE   FOR  THE  DETECTION  OF  THE  ALKALOIDS 
AND  ALKALOID  SALTS  USED  IN  MEDICINE. 

Note. — Aconitine  is  omitted  because  it  can  only  be  really  detected  by  experiments  upon 
animals.  Salicine,  acetanilide,  and  antipyrin,  although  not  alkaloids,  are 
included,  as  they  give  tests  apt  to  be  mistaken  for  certain  alkaloids. 

IN  this  course  not  more  than  two  definite  tests  for  each  alkaloid  are  recorded, 
and  for  the  remaining  tests  the  reader  is  referred  to  the  full  table  facing  p.  87. 

Step  I.  Heat  on  platinum  foil.  If  the  substance  at  once  takes  fire  and 
burns  away  with  a  smoky  flame  and  an  odour  of  singed  hair,  it 
is  probably  an  alkaloid. 

Step  II.  To  a  solution  of  the  substance  in  water  or  dilute  acid  add : — 

(a)  Mayer's  solution  (see  mdex),  which  gives  a  precipitate  with  all 
official  alkaloids  (except  caffeine),  but  no  effect  with  antipyrin. 

(b]  Solution  of  potassium  bismuthous  iodide*  which    will    give    a 
precipitate  with  all  official  alkaloids,  also  with  acetanilide  and 
antipyrin. 

Step  III.  Put  a  piece  of  red  litmus  paper  on  a  watch-glass,  lay  on  to 
this  a  little  of  the  substance,  and  moisten  it  with  a  few  drops  of 
strong  rectified  spirit.  If,  on  standing  for  a  short  time,  the 
paper  is  rendered  blue,  we  are  dealing  with  a  free  alkaloid ;  if 
not,  then  it  is  an  alkaloid  salt,  and  in  the  latter  case  we  shall 
have  to  search  for  the  acid  as  well  as  the  base. 

Note. — Acetates  of  alkaloids  often  become  basic  and  consequently  alkaline  by 
keeping,  so  beware  of  this. 

Step  IV.  To  a  fragment  of  a  substance  on  a  watch-glass  (placed  over 
white  paper)  add  a  drop  of  strong  H2SO4,  and  stir.  A  bright 
red  =  Salicine  and  a  deep  red  =  Veratrine. 

Confirm  former  by  warming  with  H.,SO4  +  KjCr/D;  =  odour  of  meadow- 
tweet  (salicylic  aldehyd),  and  latter  by  its  giving  yellow  with  HNO,  and 
blood-red  on  warming  with  HC1. 

Note.—  Many  alkaloids  give  pale  dirty  pinks  with  H2SO0  which  are  to  be  disregarded. 

*  Made  by  mixing  43  c.c.  of  liquor  bismuthi  with  9  grms.  of  KI  and  9  c.c.  of  strong 
hydrochloric  acid. 

84 


DETECTION  OF  THE  ALKALOIDS.  85 

Step  V.  To  the  liquid  in  which  H2SO4  has  given  no  distinct  red  add  a 
small  fragment  of  powdered  ammonium  molybdate,  and  stir. 

(a)  Greenish  purple}  _  Morphine  or  Apomorphine. 

Greenish  black  j 

Confirm  by  adding  H  NO3  to  another  fragment,  when  orange-red  ==•  morphine 
and  blood-red  =  apomorphine.  Morphine  with  FeaCl6  gives  greenish  blue, 
and  apomorphine  gives  deep  red.  Morphine  with  H2SO4  +  Na2HAsO4=* 
bluish  green. 

(b)  Bright  orange-red  =  Brucine. 

Confirm  by  testing  another  fragment  with  HNO3  and  getting  a  bright 
red,  turned  to  violet  on  warming  with  SnCl^ 

(c)  Bright  greenish  blue  =  Codeine. 

Confirm  by  HNO3  —  yellow  ;  and  by  H2SO4  +  Fe2Cl8  =  intense  blue, 
turned  scarlet  by  a  trace  of  HNO3. 

(d}  A  yellowish-green  =  Physostigmine, 

Confirm  by  adding  HNO3  to  another  portion.  A  strong  gamboge 
yellow  =  physostigmine.  Further  confirm  by  getting  a  red  with  KHO, 
becoming  blue  on  evaporating  to  dryness  on  the  water-bath,  and  the  residue 
dissolving  in  HC1  to  a  dichroic  solution. 

(e)  Evanescent  green,  changing  to  buff,  with  pale  green  streaks  = 
Hydrastinine. 

Confirm  by  testing  with  HNO3  =  pale  yellow,  becoming  orange,  and 
suddenly  red  on  adding  a  drop  of  H2SO4. 

Step  VI.  Treat  another  fragment  with  a  drop  of  H2SO4  as  before,  then 
let  another  drop  fall  near  it.  Into  the  second  drop  put  a 
fragment  of  powdered  potassium  bichromate,  let  it  digest  a 
moment,  and  then  stir  the  drops  together. 

(a)  Beautiful  violet  (evanescent)  =  Strychnine  or  Acetanilide. 

To  distinguish  between  these  we  test  original  substance  with  HNO,, 
which  gives  no  colour  with  strychnine,  but  a  dirty  yellow  with  acetanilide, 
turned  red  by  NH4HO.  (Further  confirmatory  tests,  see  page  88.) 

(b)  An  evanescent  dirty  red,  following  by  pinkish  buff  and  gradual 
formation  of  green  streaks  =  Cocaine. 

(1)  Confirm  by  mixing  5  c.c.  of  a  2  per  cent,  solution  with  5  drops  of  a 
5  per  cent,  solution  of  chromic  acid,  and  get  a  yellow  precipitate,  redissolving 
onshaking.  Nowadd  i  c.c.  HCl,and  get  a  permanent  orange-yellow  precipitate. 

(2)  Moisten  with  HNO3,  dry,  and  add  a  drop  of  alcoholic  KHO,  and  get 
odour  of  peppermint. 

Note. — A  minute  drop  of  a  dilute  solution  of  cocaine  placed  upon  the  tongue  will 
cause  tingling  and  numbness.  (Aconitine,  which  also  causes  tingling  in  the 
tongue,  gives  a  red  crystalline  precipitate  with  K.,Mn2O8  in  the  most  dilute 
solutions  (i  in  4000)  acidulated  with  acetic  acid,  while  cocaine  does  not, 
unless  present  in  amounts  over  i  per  cent. 

(c)  A  vivid  emerald-green  =  Pilocarpine. 

Confirm  by  testing  with  HNO3  and  getting  a  faint  green. 

(d)  Faint  yellowish  greens  more  decided  on  standing  =  Atropine, 
Caffeine,  Hyoscine,  Homatropine,  or  Hyoscyamine,  and  indeed 
many  alkaloids;  but  at  this  stage  test  only  for  the  following, 
and  if  not  found  pass  on  to  Step  VII. 

(1)  Atropine  warmed  with  H2SO4  gives  a  roseate  odour  ;  on  adding  K2Cr2O7the 
odour  suggests  bitter  almond  oil.     Alcoholic  solution  warmed  with  HgCl2  = 
yellow,  turning  red  ;  dissolved  in  HNO3,  and  dried  on  water  bath,  gives 
residue,  turned  violet  by  alcoholic  KHO. 

(2)  Caffeine  dissolved  in  a  c.c.  of  HC1,  a  little  KC1O3  added,  and  the  whole 
evaporated  to  dryness  on  a  water-bath,  leaves  a  residue  which   becomes 

purple  when  exposed  to  the  fumes  of  NH3,  which  colour  is  deepened  to 
violet  by  KHO. 

(3)  Hyoscine  treated  with  HNO3,  etc.,  as  for  atrop'.ne.  gives  orange-red  on  stirring 
well.     An  aqueous  solution  is  precipitated  by  KHO,  but  not  by  NH4HO. 

(4)  Homatropine  similarly  treated  to  atropine  (HNO3,  etc.)  gives  a  yellow  instead 
of  a  violet.     Shaken  out  from  its  salts  with  NH4HO  and  chloroform,  and 
the   latter   evaporated,    leaves   a    residue,    turned  first  yellow,    and    fir.ally 
brick-red,  with  a  2  per  cent,  solution  of  HgCL,  in  proof  spirit. 


86          QUALITATIVE  DETECTION  OF  ALKALOIDS,  ETC. 

(5)  Hyoscyamint.  An  aqueous  solution  acidulated  with  HC1  is  not  precipitated 
by  PtCl4,  but  is  by  AuCl3,  and  this,  when  dissolved  in  boiling  HaO,  acidulated 
with  HC1,  and  crystallised,  yields  lustrous  golden-yellow  scales  (distinction 
from  atropine}. 

Step  VII.  Dissolve  some  of  the  original  substance  in  water  (using  a 
drop  or  two  of  acetic  acid  to  help  solution  if  necessary),  then 
add  chlorine  water  and  a  gradual  excess  of  NH4HO. 

(a)  A  clear  green  solution  =  Quinine  or  Quinidine. 

(b)  A  white  precipitate  =  Cinchonine,  Cinchonidine,  or  Sparteine. 

(c)  A  clear  yellow  =  Phenazone  (Antipyrin).     (Confirm  by  nitrite 
test,  see  page  90.) 

Note. — In  presence  of  salicylate  the  ordinary  tests  for  quinine  fail,  and  in  this  case  it 
is  necessary  to  dissolve  in  dilute  hydrochloric  acid,  shake  up  with  ether  to 
remove  salicylic  acid,  and  then  draw  off  the  watery  solution  from  beneath 
the  ether  and  test  it  for  quinine. 

Separation  of  the  Cinchona  alkaloids  from  each  other. — Dissolve  in  a  little  water 
by  the  aid  of  a  few  drops  of  dilute  HC1,  heat  nearly  to  boiling  and  drop  in 
dilute  NaliO  until  the  liquid  is  as  nearly  neutral  as  possible  to  litmus  paper, 
and  no  more  than  a  mere  trace  of  permanent  turbidity  is  produced  ;  cool 
perfectly  and  then  stir  in  saturated  solution  of  Rochelle  salt  until  precipita- 
tion ceases.  When  the  precipitate  has  settled  filter  out  the  tartrates  of 
Quinine  and  Cinchonidine  so  produced.  To  the  nitrate  add  a  little  spirit, 
and  stir  in  saturated  solution  of  KI  to  precipitate  the  Quinidine.  Again 
filter,  add  solution  of  ammonia  in  excess  and  shake  up  with  a  little  ether, 
when  Cinchonine  will  precipitate,  and  any  amorphotis  alkaloid  present  will 
pass  into  the  ether. 

To  separate  Quinine  and  Cinchonidine. — Take  the  tartrates  obtained  as  above, 
dissolve  in  a  little  water  with  sufficient  HC1,  place  in  a  stoppered  tube 
immersed  in  cold  water,  and  then  add  sufficient  ether,  so  that,  after  shaking 
and  again  coming  to  rest,  there  shall  just  be  a  visible  layer  of  ether  over 
the  liquid  in  the  tube.  Now  add  excess  of  NaHO,  again  shake,  cool, 
and  see  that  a  visible  layer  of  ether  still  separates,  but,  should  it  not  do  so, 
a  little  more  ether  must  be  added  and  the  whole  once  more  shaken.  The 
closed  tube  is  now  to  be  left  in  the  cold  for  some  time,  and  if  the  whole  of 
the  precipitated  alkaloid  remains  dissolved  hi  the  ether,  then  it  was  all 
Quinine,  but  if  a  crystalline  deposit  forms  at  the  base  of  the  ether  layers 
Cinchonidine  is  present. 

To  distinguish  Sparteine  from  Cinchonine.— If  25  c.c.  of  ether  be  added  to  about 
O'l  grm.  of  sparteine  sulphate  in  a  test-tube,  then  a  few  drops  of  dilute 
ammonia  water,  so  that  the  latter  shall  not  be  in  excess,  and  an  ethereal 
solution  of  iodine  (i  in  50)  be  afterwards  added  until  the  liquid,  when  shaken, 
turns  from  an  orange  to  a  dark  reddish-brown  colour,  the  bottom  and  sides 
of  the  test-tube  will  after  a  short  time  be  found  coated  with  minute,  dark 
greenish-brown  crystals,  distinctly  seen  with  a  lens  after  the  liquid  has  been 
poured  out.  (U.S. P.] 

Step  VIII.  If  we  are  dealing  with  an  alkaloid  salt  we  must  now  proceed 
to  test  the  acid.  The  ordinary  alkaloidal  salts  of  commerce  are 
chloride,  sulphate,  acetate,  phosphate,  tartrate,  citrate,  meconate, 
nitrate,  and  salicylate. 

The  first  step  will  be  to  dissolve  a  little  of  the  alkaloid  salt  in 
very  dilute  HNO3,  and  test  ( i)  for  HBr  with  Cl  water  and  chloro- 
form ;  (2)  for  HC1  by  AgNO3 ;  (3)  for  H2SO4  by  BaC)2 ;  (4)  for 
HsPO4  by  excess  of  ammonium  molybdate  and  HNOs- 

The  next  will  be  to  dissolve  in  water  only,  and  test  with 
Fe2Cle  for  acetate  or  meconate  (red)  or  salicylate  (violet). 
(Acetate  decolourised  by  boiling,  meconate  not  so ;  also  acetate 
gives  no  precipitate  with  Pb(C2H3O2)2,  and  meconate  does.) 

Lastly,  we  must  test  in  the  usual  way  for  a  tartrate  (with 
morphine)  a  citrate  (unless  the  base  be  caffeine,  this  is  not  likely), 
also  for  a  nitrate  (especially  with  pilocarpine  and  strychnine), 
and  finally  for  a  valerianate  (with  quinine). 


DETECTION  OF  CERTAIN  ORGANIC  BODIES.  87 


GENERAL   R&SUM6   OF    THE    TESTS    FOR    ALL   THE   CHIEF 

ALKALOIDS. 

The  following  table  is  given  by  Dragendorff  in  his  "  Pflanzenanalyse."     The 
author  has  found  it  to  be  fairly  accurate,  except  in  the  case  of  aconitine. 
The  following  are  the  reagents  used  : — 

1.  Pure  strong  sulphuric  acid  free  from  nitrous  fumes. 

2.  200  parts  of  sulphuric  acid  with  i  part  of  nitric  acid. 

3.  *i  gramme  of  sodium  molybdate  in  10  c.c.  strong  sulphuric  acid 

(Frohde's  test). 

4.  i  part  alkaloid  mixed  with  5  parts  powdered  white  sugar,  and  then 

strong  sulphuric  acid  dropped  on. 

5.  Sulphuric  acid  and  potassium  bichromate  used  as  already  described 

in  Division  A. 

6.  Nitric  acid  (strong  1*3  sp.  gr.). 

7.  Strongest  fuming  hydrochloric  acid. 

8.  Ordinary  solution  of  Fe2Cl6  as  neutral  as  possible. 

The  reagents  being  generally  added  in  turn  to  a  fragment  of  the  dry 
alkaloid,  or  to  the  residue  left  on  the  evaporation  of  an  alkaloidal 
solution. 


DIVISION  B.  QUALITATIVE  DETECTION  OF  CERTAIN  ORGANIC 
BODIES  COMMONLY  EMPLOYED  IN  MEDICINE  AND  IN  THE 
ARTS. 

I.  The  substance  is  a  liquid  usually  having  a  characteristic  odour,  and 

entirely  volatile  by  a  gentle  heat. 
Note. — These  odours  should  be  carefully  studied  on  known  samples. 

Acetic  Ether  (ethyl  acetate).  Miscible  with  alcohol,  slightly  with  water 
(i  in  10).  Distilled  with  KHO  gives  alcohol  (proved  by  Leiberfs 
test),  and  the  residue  in  the  retort  yields  the  reactions  for  ar> 
acetate. 

Amyl  Alcohol  (fousel  oil).  Miscible  with  alcohol,  but  sparingly 
soluble  in  water,  on  which  it  floats.  Does  not  volatilise  under 
128°  C.  Gently  warmed  with  sodium  acetate  and  diluted 
H2SO4  it  gives  the  odour  of  pears.  Distilled  with  K2Cr2O7  +• 
H2SO4,  and  the  distillate  boiled  with  KHO,  potassium  valerianate 
is  formed,  giving  the  tests  for  valerianates. 

Amyl  Nitrite.  Miscible  with  alcohol  but  not  with  water,  on  which  it 
floats.  Dropped  into  fused  KHO  it  forms  potassium  valerianate. 
Shaken  up  with  a  solution  of  KI,  acidulated  with  diluted 
H2SO4,  iodine  is  liberated  and  NO  is  evolved. 

Benzol  (benzene).  Miscible  with  alcohol  but  not  with  water,  upon 
which  latter  it  floats.  Dropped  into  HNOs  it  yields  nitro- 
benzene, having  an  odour  of  bitter  almonds.  Dropped  into' 
H2SO4  and  the  solution  boiled  with  KHO  a  carbolate  is* 
obtained  and  may  be  tested  for. 

Benzinum  (petroleum  spirit).  Miscible  with  alcohol,  but  insoluble  iny 
and  lighter  than,  water.  Does  not  give  reactions  with  HNOs, 
H2SO4,  and  KHO  (distinction  from  benzene]. 

Chloroform.  Miscible  with  alcohol.  Very  slightly  soluble  in,  and 
heavier  than,  water.  Reduces  Fehling's  solution.  Boiled  with 


88  QUALITATIVE  DETECTION  OF  ALKALOIDS,   ETC. 

KHO  and  a  fragment  of  resorcin  gives  an  intense  red  (rosolic 
add] ;  add  a  drop  of  aniline  to  'Some  alcoholic  solution  of 
KHO,  then  add  a  drop  or  two  of  the  suspected  liquid  and 
boil,  when  a  fearfully  offensive  odour  of  phenyl-isocyanide  is 
produced. 

Creasote  (chiefly  guaiacol  and  creasol).  Very  slightly  soluble  in  water, 
in  which  it  sinks.  The  aqueous  solution  gives  a  green  colour 
with  ferric  chloride,  rapidly  changing  to  a  reddish-brown 
precipitate.  Creasote  is  miscible  with  collodion  without  pro- 
ducing any  turbidity,  and  it  is  insoluble  in  cojnmercial  glycerine. 
(distinction  from  liquid  carbolic  acid}. 

Ethyl  Alcohol.  Add  K2Cr2O:  and  H2SO4  and  boil,  and  get  a  green 
colour  and  odour  of  aldehyd ;  heat  with  NaC2H3O2  and  H2SO4, 
and  get  odour  of  apples ;  warm  with  KHO  and  iodine,  and  get 
yellow  precipitate  of  iodoform  (Leiberis  test — best  done  on  a 
portion  that  has  been  distilled  off  from  the  original  liquid). 

Glycerine.  Colourless  and  odourless  syrupy  liquid,  volatilising  on 
heating  with  very  irritating  vapours.  A  borax  bead  dipped  in 
glycerine  and  held  in  the  Bunsen  flame  colours  it  green  (if 
the  original  liquid  be  acid  it  must  be  first  neutralised  and 
ammonium  salts  must  be  absent).  Two  drops  of  concentrated 
glycerine  heated  to  125°  C,  with  two  drops  each  of  phenol 
and  H2SO4,  yield  a  semi-solid  mass  which  dissolves  in 
dilute  ammonia  solution,  giving  a  carmine  colour.  Before 
these  tests  are  used  for  any  mixture,  it  should  be  evaporated 
to  dryness  with  excess  of  slaked  lime  at  a  temperature  under 
1 00°  C.,  and  the  residue  having  been  extracted  with  a  mixture 
of  equal  volumes  of  absolute  alcohol  and  ether,  the  resulting 
solution  should  be  evaporated  on  a  water-bath,  and  the  tests 
applied  to  the  residue. 

Jlfethyl  Alcohol.  To  5  c.c.  of  the  liquid  add  2  grammes  of  K2Cr2O7, 
and  20  c.c.  of  dilute  H2SO4  (i  in  4);  let  the  whole  stand  for 
twenty  minutes,  and  then  distil  off  10  c.c.  Neutralise  this  dis- 
tillate with  Na2COs,  evaporate  to  a  low  bulk,  acidulate  with 
acetic  acid,  and  apply  the  tests  for  formate  (page  46). 

Nitrobenzene  (oil  of  mirbane).  Yellowish  oily  liquid  having  an  odour 
of  bitter  almonds.  Placed  in  contact  with  zinc  dust  and 
diluted  H2SO4,  it  is  reduced  to  aniline.  If  a  crystal  of  KC1O3 
be  dropped  in  and  H2SO4  run  down  the  tube  (as  in  testing  for 
nitrates)  a  violet  colour  is  produced  round  the  crystal. 

Paraldehydum  (paraldehyd).  Soluble  in  water  (i  in  10);  miscible  with 
ether;  no  colour  with  KHO  after  standing  (dist.from  aldehyd}. 
Mirror  on  warming  with  ammonio-argentic  nitrate. 

II.  The  substance  is  a  solid  which  chars  on  heating  and  entirely  burns 
away.  Observe  the  colour  of  the  substance,  try  its  solubility, 
first  in  cold  water  and  then  in  cold  chloroform,  and  apply  the 
following : — 

Case  (A).  Substance  white,  difficultly  soluble  (or  insoluble)  in  cold 
water,  but  readily  in  chloroform.  Suspect  and  test  for : — 

Acetanilide  (antifebrin).  Slightly  soluble  in  cold  water  (neutral  reaction); 
freely  soluble  in  chloroform,  ether,  benzol,  and  rectified  spirit. 
Heated  with  solution  of  KHO  and  a  drop  of  chloroform,  the 
odour  of  phenyl-isonitrile  is  developed.  Aqueous  solution  gives 
yellowish-white  precipitate  with  bromine  water  (distinctions  from 
fihe.nacetin). 


DETECTION  OF  CERTAIN  ORGANIC  BODIES.  89 

A  cold  solution  gives  no  colour  with  Fe2Cl6  (distinction  from 
antipyrin,  acetone,  and  aniline  salts).  No  colour  with  H2SO4. 

Elaterin.  In  greenish-white  friable  masses.  Insoluble  in  water,  but 
soluble  in  chloroform.  With  a  drop  of  liquefied  carbolic  acid 
and  two  drops  of  H2SO4  gives  first  crimson  and  then  scarlet. 

Naphtol  (beta-naphthol).  Often  buff  or  yellow  when  old  stock.  Slightly 
soluble  in  water,  freely  in  chloroform,  and  has  a  slight  odour 
of  phenol.  Hot  saturated  solution  with  i  drop  of  solution  of 
NH3  has  a  pale  blue  fluorescence.  OT  grm.  added  to  5  c.c. 
aqueous  KHO  (i  in  4)  with  i  c.c.  chloroform,  and  gently 
warmed,  the  aqueous  layer  goes  first  blue,  then  green,  and  finally 
brown.  o'i  grm.  in  10  c.c.  boiling  H2O,  mixed  with  10  c.c.  of 

3  per  cent,   solution  of  Fe^Cle,  gives  a  precipitate  becoming 
brown,  but  not  violet  (absence  of  alpha-naphthol). 

Picrotoxinum  (picrotoxin).  Slightly  soluble  in  water,  freely  in  chloro- 
form ;  soluble  in  10  parts  of  a  solution  of  KHO,  and  the  liquid 
reduces  Fehling's  solution ;  H2SO4  gives  a  saffron-yellow ;  its 
solution  is  not  precipitated  by  HgCl2,  by  bismuth  potassium 
iodide,  PtCl4,  or  by  tannic  acid  (showing  that  it  is  not  an 
alkaloid). 

Salol  (phenol  salicylate).  White  crystalline  powder.  Almost  insoluble 
in  water,  but  freely  in  chloroform.  On  melting  together  salol  and 
NaHO,  and  then  rendering  acid  with  HC1,  crystals  of  salicylic 
acid  separate,  and  the  odour  of  phenol  is  obtained.  If  a  few 
drops  of  very  dilute  Fe2Cle  be  added  to  10  c.c.  alcoholic  solution 
of  salol  a  violet  is  produced.  Water  that  has  been  shaken  with 
salol  gives  no  colour  with  Fe2Cl6  (absence  of  free  salicylic  acid}. 

Sa?itonin.  White  when  fresh,  pale  yellow  when  old ;  nearly  insoluble 
in  water,  soluble  in  alkali ;  added  to  a  warm  alcoholic  solution 
of  KHO  gives  a  violet-red  colour,  gradually  fading  away; 
added  to  i  c.c.  of  H2SO4  and  a  few  drops  of  Fe2Cl6  and  heated 
gives  a  red  colour  changing  to  brown.  (These  will  detect  santonin 
in  urine.)  Heated  on  a  porcelain  dish  and  H2SO4  added  gives 
a  purple. 

Sulphcnal.  Slightly  soluble  in  cold  water  and  in  chloroform ;  fused 
with  an  equal  weight  of  KCN  the  odour  of  mercaptan  is  evolved, 
and  the  residue  dissolved  in  water,  acidulated  with  HC1  and 
FesCle  added,  a  red  colour  is  produced ;  a  solution  mixed  with 

4  drops  of  carbolic  acid,  and  strong  H2SO4  added  till  the  liquid 
boils,  a  green  colour  is  obtained.     Heated  in  air  gives  off  S02, 
or  with  dried  NaC2H3O2  gives  H2S. 

Case  (B).  Substance  white,  not  readily  soluble  in  cold  water  or  cold 
chloroform.  Suspect  and  test  for : — 

Glusidum  (saccharine  or  benzoyl-sulphonic  imide).  Not  readily  soluble 
in  cold  water  or  in  chloroform ;  heated  to  redness  with  Na2COa 
it  chars  and  gives  off  an  odour  of  benzene ;  not  blackened  by 
H2SO4;  on  fusing  with  NaHO,  cooling,  dissolving  in  water, 
faintly  acidulating  with  HC1,  and  adding  Fe2Cl6,  a  reddish 
purple  is  obtained. 

Phenacetinum  (phenacetin).  Only  slightly  soluble  in  cold  water,  and 
not  freely  in  chloroform.  A  hot  solution  gives  a  violet  with 
chlorine  water,  fading  to  red ;  boiled  with  HC1  and  Fe2Cle 
added  gives  a  red ;  mixed  with  four  drops  of  carbolic  acid,  and 
H2SO4  added  till  the  liquid  boils,  gives  a  purplish-brown  colour 
and  odour  of  acetone;  o'i  grm.  boiled  with  2  c.c.  of  HC1  for 


90          QUALITATIVE  DETECTION  OF  ALKALOIDS,  ETC. 

\  minute,  and  the  liquid  diluted  with  10  volumes  of  water,  cooled 
and  filtered,  gives  a  deep  red  with  solution  of  chromic  acid ; 
does  not  give  precipitate  with  bromine  water,  nor  does  it  give 
the  isonitrile  test  (dist.  from  acetanilide).  0*3  grm.  in  i  c.c. 
90  per  cent,  alcohol,  diluted  with  3  c.c.  water  and  boiled  with  i 
drop  yjj-  iodine  solution,  gives  no  red  (absence  of paraphenetidin). 

Case  (C).  Substance  white  (crystalline),  and  readily  soluble  in  cold 
water.  Suspect  and  test  for  : — 

Chloral  (hydrous).  Soluble  in  water.  Heated  with  solution  of  KHO 
gives  odour  of  chloroform,  and  the  contents  of  the  tube  give 
the  reactions  of  a  formate  (page  46).  Gives  the  same  test  with 
resorcin  as  chloroform.  Mixed  with  a  5  per  cent,  solution  of 
carbolic  acid,  and  an  equal  bulk  of  H2SO4  added,  gives  a  pink. 

Phenazonum  (antipyrin  or  phenyl-methyl-pyrazolone).  Freely  soluble 
both  in  water  and  chloroform ;  with  NaNC>2  and  diluted  sul- 
phuric acid  gives  a  green ;  an  aqueous  solution  with  an  equal 
volume  of  HNOs  is  yellow,  passing  to  crimson  on  warming; 
Fe2Cle  gives  a  deep  red,  discharged  by  dilute  H2SO4.  2  c.c. 
of  a  i  per  cent,  aqueous  solution  with  2  drops  of  HNOs  goes 
green,  changed  to  red  by  adding  3  drops  more  and  boiling. 

Resorcin.  Freely  soluble  in  water ;  Fe2Cl6  added  to  an  aqueous 
solution  gives  violet,  discharged  by  NH4HO ;  Na2OCl2  gives 
a  violet,  fading  to  yellow;  NH4HO  and  CaOCl2  gives  a  red 
violet,  turning  yellow. 

Soluble  Saccharine.  Tests  as  for  glusidum,  but  when  heated  to  redness 
leaves  a  residue  giving  the  tests  for  sodium. 

Sugars.  (a)  Sucrose  (cane  sugar).  A  solution  boiled  with  dilute 
H2SO4  darkens  markedly,  but  not  when  boiled  with  liquor 
potasses.  Trommer's  test  (a  few  drops  of  solution  of  CuSO4 
with  an  excess  of  KHO  and  boiled)  gives  no  red.  Fehling's 
solution  (see  p.  129)  gives  no  red. 

(b)  Glucose  (grape  sugar).      A  solution  gives  no  darkening 
when  boiled  with  dilute  H2SO4,  but  darkens  when  boiled  with 
liquor  potasses.     Trommer's  and  Fehling's  tests  both  give  a  red 
precipitate. 

(c)  Lactose  (milk  sugar).     A  solution  is  only  slightly  affected 
either   by  boiling  with    dilute    H2SO4  or  with  liquor  potassce. 
Fehling's  and  Trommer's  tests  both  give  a  red  precipitate. 

Case  (£>).     The  substance  is  coloured.     Suspect  and  test  for : — 

Adeps  Lance  (cholesterin-fat).  Insoluble  in  water,  soluble  in  chloro- 
form and  ether,  sparingly  in  rectified  spirit.  The  chloroformic 
solution  poured  gently  over  the  surface  of  strong  H2SO4  gives 
a  purple ;  five  grammes  in  ethereal  solution  mixed  with  phenol- 
phthalein  give  a  red  on  the  addition  of  '2  c.c.  of  normal  sodium 
hydrate  (distinction  from  ordinary  fatty  acids,  which  would 
saponify  and  absorb  much  more  soda).  Soluble  in  boiling 
alcohol,  and  crystallises  out  on  cooling. 

Aloin.  Yellow  and  slightly  soluble  in  cold  water,  freely  in  hot ; 
insoluble  in  ether.  HNOs  gives  a  red  (except  with  socaloin, 
which  goes  brownish).  Dissolve  in  strong  H2SO4  and  a  few 
drops  HNOs,  dilute  with  water,  and  get  a  yellow,  turned  deep 
claret  by  excess  of  NH4HO.  H2SO4  on  a  fragment  of  aloin, 
and  a  rod  moistened  with  HNOs  held  near,  gives  a  blue  with 
nataloin  only. 

Chrysarobin.     A  brownish-yellow  powder,  partly  volatile  by  heat  with 


QUALITATIVE  ANALYSIS  OF  SCALE  PREPARATIONS.      91 

yellow  vapours;  insoluble  in  water,  but  soluble  in  KHO,  gradu- 
ally producing  a  brilliant  red.  H2SO4  on  the  fragment  gives  a 
reddish  brown. 

Fel  Bovinum  (ox  bile).  Yellowish-green  substance,  soluble  in  water 
and  spirit.  A  solution  mixed  with  a  drop  of  syrup  and  then 
H2SO4  cautiously  added  becomes  cherry-red,  changing  suc- 
cessively to  carmine,  purple,  and  violet. 

Gelatinum  (gelatine).  Swells  up  in  water,  soluble  on  boiling.  Tannic 
acid  gives  a  flocculent  precipitate ;  HgCl2  gives  a  white ;  not 
precipitated  by  dilute  acids,  alum,  plumbic  acetate,  or  ferric 
chloride. 

Guaiacum  Resin.  In  powder  yellowish  green.  Insoluble  in  H2O,  but 
soluble  in  alcohol,  and  this  solution  becomes  blue  with  Fe2Cl6 
or  solution  of  H2O2.  The  H2SO4  +  H2O  test  (see  Jalap  Resin) 
gives  a  characteristic  odour  somewhat  balsamic. 

lodoform.  Yellow,  insoluble  in  water,  and  characteristic  odour ;  warmed 
with  alcoholic  solution  of  KHO,  and  then  mixed  with  starch 
paste  and  excess  of  HNOs,  gives  a  blue.  (May  be  detected  in 
urine  by  adding  alcohol  and  pouring  upon  phenol-potassium 
contained  in  a  test-tube,  when  the  red  colour  will  cover  the 
bottom  of  the  tube  ;  soluble  in  alcohol.) 

Jalap  Resin.  Dark  brown  in  fragments,  paler  in  powder.  Insoluble  in 
water,  but  soluble  in  alcohol ;  insoluble  in  turpentine.  H2SO4 
dropped  on  a  fragment  turns  ij;  reddish,  and  on  adding  a  few 
drops  of  water,  so  as  to  cause  evolution  of  steam,  the  charac- 
teristic odour  of  jalap  is  observed.  Only  10  per  cent,  should 
be  soluble  in  ether  (absence  of  scammony  or  Tampico  jalap  resins). 

Podophyllin.  Pale  yellow  to  orange-brown.  Insoluble  in  water,  but 
soluble  in  spirit ;  soluble  in  NH4HO ;  H2SO4  on  a  fragment 
slightly  colours  it,  and  on  adding  a  drop  or  two  of  water  no 
characteristic  odour  is  evolved.  Partly  soluble  in  ether. 

Resin.  Insoluble  in  water,  soluble  in  alcohol  and  in  turpentine ; 
H2SO4  on  a  fragment  gives  a  strong  red,  and  on  adding  a  few 
drops  of  water,  so  as  to  cause  evolution  of  steam,  the  character- 
istic odour  is  observed. 

Scammony  Resin.  Brownish  translucent  fragments.  Insoluble  in  H2O, 
but  soluble  in  alcohol,  and  completely  in  ether  (distinction  from 
ialap  resin).  Alcoholic  solution  gives  no  colour  with  Fe2Cle 
or  H2Oa  (absence  of  guaiacum  resin).  The  H2SO4  +  H2O  test 
gives  the  odour  of  scammony. 

DIVISION  C.     QUALITATIVE  ANALYSIS  OF  SCALE  PREPARATIONS. 

Step  I.     Heat  a  little  to   redness   on   platinum  foil,  and   observe  the 
following  possible  cases  : — 

(a)  If  it  entirely  burns  suspect  Beberine  sulphate. 

Confirm  by  testing  for  sulphate  by  BaQ2 ;  and  for  beberine  with  KHO, 
getting  a  yellowish- white  precipitate  entirely  dissolved  by  agitating  the  liquid 
with  twice  its  volume  of  ether.  This  ethereal  liquid  evaporated  leaves  a 
yellow  residue  entirely  insoluble  in  dilute  HC1. 

(b)  An  ash  is  left :  (a)  Put  a  small  fragment  of  the  ash  upon  a  piece  of 

red  litmus  paper,  moisten  it  with  a  drop  of  water,  and,  if  it 
turns  the  paper  blue,  suspect  potassium;  (b)  Dissolve  the 
remainder  of  the  ash  in  nitric  acid,  dilute  and  test  with  excess 
of  ammonium  molybdate  for  phosphoric  acid. 

Note. — If  K  be  suspected,  prove  it  by  igniting  some  more  of  the  scale,  extracting  the 
ash  with  very  little  boiling  water,  filtering,  cooling,  and  adding  PtCl4. 


92          QUALITATIVE  DETECTION  OF  ALKALOIDS,  ETC. 

Step  II.  Make  a  weak  solution  of  the  scale,  acidulate  it  with  a  drop  of 
HC1,  and  test  for  ferrous  iron  with  K6Fe2Ci2Ni2,  and  for  ferric 
with  K^FeCeNg.  Also  test  another  portion  by  adding  excess  of 
AgNO3,  and  heating,  when  reduction  to  black  or  a  mirror  « 
tartrate. 

Step  III.  To  a  strong  solution  add  excess  of  NaHO,  boil,  and  smell  for 
ammonia.  If  neither  phosphoric  nor  tartaric  acid  has  been 
already  found,  filter  out  the  precipitated  ferric  hydrate  and  use 
the  filtrate  for  testing  for  acids  as  follows  : — 

(a)  Test  a  portion  for  citric  acid  exactly  as  directed  in  the  organic  acid 

course  (page  80). 

(b)  Test  another  portion  by  exactly  neutralising  with  HNOs,  and  adding 

AgNOs,  when  a  white  precipitate  =  pyrophosphate,  and  the  same 
turning  black  =  hypophosphite, 

Of  course  this  step  is  never  to  be  taken  unless  an  indication  of  P  be  got 
in  the  ash  with  molybdate  in  Step  I. 

Step  IV.  Make  a  solution  of  a  fair  amount  of  the  scale,  add  a  drop  or 
two  of  very  dilute  NH4HO,  and  then  add  some  strong  NH4HO. 

Case  (A).  There  is  either  no  precipitate,  or  it  dissolves  in  strong 
NH4HO :  Add  some  chloroform  and  shake  up.  Separate  the 
chloroform  by  a  pipette,  and  evaporate  it  to  dryness  in  two 
portions  on  separate  white  dishes.  Test  the  one  residue  for 
strychnine,  and  the  other  for  quinine. 

Case  (j9).  The  NH4HO  causes  a  permanent  white  precipitate : 
Filter  out  precipitate,  and  dissolve  it  off  the  filter  with  a  little 
warm  water  containing  a  few  drops  of  acetic  acid.  Boil  the 
solution  down  to  a  low  bulk,  cool,  neutralise  if  necessary  with 
very  dilute  NaHO,  and  then  add  a  few  drops  of  saturated 
solution  of  Rochelle  salts  and  shake,  when  a  white  precipitate 
=  cinchonidine.  If  not  that,  then  add  NH4HO,  when  a  white 
precipitate  insoluble  on  shaking  with  ether  =  cinchonine. 

DIVISION  D.     GENERAL   SKETCH  OF  THE  METHOD   OF  TESTING 
FOR  POISONS   IN  MIXTURES. 

This   course   is   only   carried   down   to   the  best   method  of  preliminary 
procedure  for  the  isolation  of  the  poison,  all  the  individual  tests  to  be  after- 
wards applied  having  been  already  fully  described  in  this  or  former  chapters. 
Note. — Students  desiring  to  study  the  subject  more  deeply  are  referred  to  Dr.  Leyda's 
articles  on  detection  of  poisons  in  the  Analyst  for  1890. 

Step  I.  If  the  liquid  be  very  strongly  acid,  and  effervesces  violently  with 
NaHCOs,  test  for  poisonous  acids,  specially  for  Nitric  and 
Oxalic. 

Note. — Oxalic  acid  is  best  separated  from  a  mixture  by  precipitation  with  plumbic 
acetate,  filtering,  suspending  the  precipitate  in  water,  and  passing  H..S  This 
removes  the  lead,  and,  after  again  filtering  out  the  PuS,  the  liquid  is 
evaporated  to  a  suitable  bulk  and  tested  for  oxalic  acid. 

Step    II.  Acidulate  with  |  of  its  bulk  of  HC1  (filter,  if  necessary),  and 

apply  Reinch's  test  for  As,  Sb,  Hg. 
Step  III.  Burn  to  ash,  dissolve  this  in  HC1  or  HNOs,  and  test  by  ordinary 

course  for  poisonous  metals,  especially  Pb,  Cu,  and  Zn. 

Step  IV.  If  the  original,  either  alone  or  when  heated  with  dilute  H2SO4, 
gives  the  odour  of  HCN,  of  carbolic  acid,  or  of  phosphorus, 
test  specially  for  them. 


METHOD   OF  TESTING  FOR  POISONS  IN  MIXTURES.      93 

The  reactions  of  HCN  have  been  given  at  page  40,  while  those  of  carbolic 
acid  are  found  at  page  51.  If  a  piece  of  filter  paper,  moistened  with  solution 
of  AgNOs,  and  suspended  in  the  neck  of  the  flask  or  bottle  containing  the 
suspected  matter,  be  not  darkened  after  warming  the  whole  to  50°  C.  for  a 
short  time,  no  phosphorus  is  there.  If  darkening  should  occur,  the  suspected 
matter  is  to  be  acidulated  with  H2SO4,  and  distilled  in  a  dark  room,  using  a 
glass  Liebig's  condenser,  when  a  luminous  ring  will  be  observed  to  form  in 
the  upper  part  of  the  condenser  tube.  If  the  suspected  matter  should  contain 
spirit  or  certain  other  volatile  bodies,  the  ring  will  not  appear  till  they  have 
passed  over. 

Step   V.  If  the  original  has  no  odour  of  opium  we  proceed  to  apply  Stas's 
process  for  the  detection  of  alkaloids  as  follows  : — 

If  the  original  be  a  solid,  it  is  operated  upon  directly,  but, 
if  a  fluid,  it  is   first  evaporated   to  dryness   on  a  water- bath. 
Add  some  strong  alcohol  and  a  small  crystal  of  tartaric 
acid,  boil,  and  filter.     Evaporate  the  filtrate  to  dryness      O 
on  the  water-bath,  and  take  up  with  warm  water  slightly  /~\ 
acidified  with  acetic  acid,  then  cool  and  filter  (if  neces-  /         J 
sary),  taking  care  that  the  liquid  just  remains  acid.     Put  V       I 
this  acid  liquid  into  a  separator  (fig.  17),  and  shake  it  \    / 
up  with  ether   or  benzene,  and  carefully  separate  the      *  ' 
ether.     (This  ether  may  contain  fat,  certain  bitter  prin- 
ciples, and  glucosides,  and  therefore,  in  a  general  in- 
vestigation of  a  drug,  it  should  not   be  rejected,  but 
evaporated,  and   the   residue  examined.)      Now  make  Flgl  I7- 
the  liquid  distinctly  alkaline  by  the  careful  addition  of  Na2COs 
or  NaHO,  and  again  shake  up  in  the  separator  with  chloroform, 
which  will  take  up  all  the  alkaloids  except  morphine.      The 
chloroform  is  separated,  evaporated  at  a  very  gentle  heat,  and 
the  residue  tested  for  alkaloids  by  the  course  given  in  Division 
A  by  the  table  facing  page  87  of  this  chapter.      Lastly,  the 
alkaline  liquid  is  shaken  up  with  warm  amylic  alcohol,  which 
extracts  morphine  and  leaves  it  upon  evaporation. 

Note. — It  is  often  better  to  get  the  alkaloids  out  from  the  chloroform  or  amylic  alcohol 
by  shaking  the  separated  solvent  up  with  water  acidulated  with  acetic  acid 
or  HC1,  thus  getting  an  aqueous  solution  of  the  alkaloid  and  leaving  any 
resinous  matters  in  the  chloroform.  The  re-treatment  of  this  solution  with 
alkali  and  chloroform,  etc.,  will  then  enable  us  to  get  the  alkaloid  in  a  state 
of  purity. 

Step  VI.  When  opium  is  suspected.  Acidulate  with  acetic  acid  and  filter, 
if  necessary  (any  alcohol  present  being  got  rid  of  by  boiling  it 
off).  Precipitate  when  cold  with  solution  of  plumbic  acetate, 
filter,  and  preserve  the  precipitate  (A)  for  examination  for 
meconic  acid  and  the  filtrate  (B)  for  morphine. 

(a]  Precipitate  (A)  is  suspended  in  water  and  treated  with  H2S  till  per- 
fectly decomposed ;  the  PbS  filtered  out,  and  the  filtrate,  after 
evaporation  to  drive  off  H2S,  tested  for  meconic  acid.  If  this 
be  found,  it  is  held  to  be  sufficient  proof  of  presence  of  opium 
taken  in  connection  with  the  odour  of  the  original. 
(l>)  Filtrate  freed  from  Pb  by  H2S  and  filtering  is  evaporated  to  dryness 
with  a  slight  excess  of  NaHCOs  on  a  water-bath.  The  residue 
will  yield  its  morphine  to  alcohol,  generally  in  a  state  suffi- 
ciently pure  to  evaporate  a  drop,  and  test.  If  not,  then  am.ylic 
alcohol  must  be  used. 


PART  II. 

QUANTITATIVE    ANALYSIS. 


CHAPTER    VI. 
WEIGHING,  MEASURING,  AND  SPECIFIC  GRAVITY. 

I.  WEIGHING  AND  MEASURING. 

ALL  bodies  mutually  attract  each  other.  As  the  earth  is  the  largest  body 
within  our  atmosphere,  it  follows  that  its  attraction  is  always  greater  than  that 
of  any  surrounding  matter.  The  force  thus  developed  is  called  the  attraction 
of  gravitation,  and  its  exercise  is  the  cause  of  weight.  Weighing  is  performed 
by  means  of  the  well-known  appliance  called  the  balance.  Figure  18 
illustrates  a  chemical  balance  of  the  modern  short-beam  type.  H  is  the 
handle  by  which  the  balance  is  put  into  action,  and  R  is  the  appliance  for 


Fig.  18. 

placing  rider  weights  upon  the  graduated  beam.     Weights  are  made  either 
according  to  the  metrical  or  the  English  system,  as  follows  : — 

(a)  The  Metrical  system. — The   metrical    weights  of   precision  above  one 
irramme  are  in  brass  ;  and  then  we  have   '5,  '2,  *i,  -i,  and  following  them 
.05,   '02,   'oi,   'oi,  all   in   platinum   or  aluminium   foil. 
The  quantities  below  'ci  (one  centigramme)  are  weighed 
by  a  rider  on  the  beam.     The  combination  of  5,  2,  i, 
and  i  has  been  chosen  because  they  have  been  found 
to  give  the  greatest  number  of  possible  combinations 
with  the  fewest  weights.     Figure  19  shows  such  a  box 
rie- »9-  of  metrical  weights  as  usually  employed  in  quantita- 

tive analysis.     The  metrical  system  is  founded  upon  the  metre.     The  metre  is 
multiplied  and  divided  entirely  by  ro,  thus  : — 


WEIGHING  AND  MEASURING.  95 


Kilo-metre IODQ- 

Hecto-metre 100- 

Deca-metre   ......  io€ 

Metre   .......  1 

Deci-metre    ...«.«  *l 

Centi-metre *oi 

Milli-metre 'OO* 

The  metre  taking  the  practical  place  of  the  English  yard,  the  decimetre 
consequently  takes  the  place  of  the  foot,  and  the  centimetre  of  the  inch ;  and 
just  as  weight  is  got  in  our  system  from  the  cubic  inch,  so  it  is  got  metrically 
from  the  cubic  centimetre,  only  much  more  simply,  because  i  cubic  centimetre 
of  distilled  water ;  measured  at  4°  C.  and  760  millimetres  bar.,  weighs  one 
gramme.  The  gramme  is  multiplied  and  divided  exactly  as  the  metre,  thus : — • 

Kilo-gramme  ..'...  iooo- 

Hecto-gramme 100- 

Deca-gramme  .....  icr 

Gramme        ......  !• 

Deci-gramme  .....  'I 

Centi-gramme -OI 

Milli-gramme 'ooi 

One  kilogramme  (1000  grammes)  of  water  at  the  standard  temperature  and 
pressure  measures  one  litre  (or  1000  cubic  centimetres),  and  we  have  therefore 
the  following  simple  relation  of  weights  and  measures  of  water  :— 

Weight.  Measure. 

1000  grammes  .        .         .         .         I  litre  or  looo  cubic  centimetres. 

100         „  ....         I  deci-litre  or  100         ,,         „ 

10         „  ....         I  centi-litre  or  10         „         „ 
I  gramme  i  milli-litre  or  I  cubic  centimetre. 

So  we  see  that  using  water  at  4°  C,  a  gramme  by  weight  and  a  cubic  centi- 
metre by  measure  amount  to  the  same  thing ;  as  likewise  do  a  kilogramme 
by  weight  and  a  cubic  decimetre  (or  litre)  by  measure.  The  relation  between 
the  two  systems  is  easily  calculated  from  the  following  standards  : — 

Metrical.  English. 

I  Gramme         =-  15-432  grains. 
I    Kilogramme  —    2-205  Ib.  (or  15.432  grains). 
I    l/tre                =     1-76  pints  (or  35  fl.  oz.,  2  drachms,  II  minims). 

I  Metre  »=  39-37  inches. 

So  that  i  decimetre  is,  as  nearly  as  possible,  4  inches  ;  and  i  decilitre,  a  trifle 
under  4  fluid  ounces. 

(b)  The  English  system. — In  weights  of  precision,  any  amount  above  10 
grains  is  usually  represented  by  a  series  of  small  brass  cylinders,  from  10  to 
j  ceo  grains  ;  then  follow  6,  3,  3,  2,  and  t  grain  in  platinum  wire,  and 
afterwards  '6,  '3,  '3,  *2,  and  'i  of  a  grain  in  platinum,  or,  more  frequently, 
in  aluminium  wire.  Quantities  of  less  than  ^  grain  are  weighed  by  a  small 
rider  of  gold  wire  placed  on  the  beam  of  the  balance.  The  foundation  of 
the  English  system  is  the  inch.  One  cubic  inch  of  distilled  water,  measured 
at  60°  F.  and  30  inches  barometrical  pressure,  weighs  252-45  grains,  or 
252^  grains  nearly.  There  are  437*5  grains  in  an  ounce,  and  16  ounces 
(or  7000  grains)  in  a  pound.  Measure  of  capacity  is  obtained  by  weighing 
out  10  Ib.  of  water  at  60°  F.  and  30  inches  bar.,  when  the  whole  measures 
one  gallon.  The  gallon  is  in  turn  divided  into  8  pints  (=  20  ounces,  or  8750 
grains  of  water,  per  pint);  the  pint  into  20  fluid  ounces  (=  437*5  grains 
of  water  per  fluid  ounce) ;  the  fluid  ounce  is  divided  into  8  fluid  drachms 
(=  54'68  grains  of  water  per  fluid  drachm)  ;  and,  lastly,  the  fluid  drachm 
is  divided  into  60  minims  ('91  grain  of  water  in  each  minim). 


96        WEIGHING,  MEASURING,  AND  SPECIFIC  GRA  VITY. 

II.    SPECIFIC  GRAVITY 

may  be  generally  explained  to  be  the  ratio  of  the  weight  of  one  thing  to  the 
weight  of  an  equal  volume  of  something  else  taken  as  a  standard.  For  liquids 
and  solids  the  standard  is  distilled  water  at  a  temperature  of  60°  F.  An  acquaint- 
ance with  the  various  cases  which  may  occur  in  the  taking  of  specific  gravity 
is  of  great  importance,  as  it  forms  an  exceedingly  ready  method  of  testing  the 
purity  and  strength  of  many  substances.  A  knowledge  of  the  specific  gravity 
of  the  various  bodies  also  enables  the  chemist  to  tell  at  once  what  any  given 
volume  of  a  liquid  ought  to  weigh,  or  conversely,  what  size  of  vessel  will  be 
required  to  contain  any  given  weight.  The  following  are  the  chief  varieties 
of  cases  which  may  occur  in  taking  : — 

(A)   Specific  Gravity  of  Liquids. 

CASE  i.  To  take  the  specific  gravity  of  a  fluid.— A  small  bottle  of  thin 
glass  is  procured,  and  counterpoised  upon  a  balance.  It  is  then  filled  with 
distilled  water  at  15-5°  C.  (60°  F.),  and  the  weight  of  the  water  thus  introduced 
noted.  The  bottle,  having  been  emptied  and  dried,  is  filled  with  the  liquid 
to  be  tested,  also  at  15*5°  C.  (60°  F.),  and  the  whole  is  again  weighed.  By 
this  means,  having  ascertained  the  weight  of  equal  bulks  of  water  and  fluid,  it 
only  remains  to  divide  the  weight  of  the  fluid  by  the  weight  of  the  water,  and 
the  quotient  will  be  the  specific  gravity  required.  To  make  the  calculation 
clear,  observe  the  following  examples  : — 

A  counterpoised  bottle  filled  with  distilled  water  weighs  100  grammes  ;  the  same  bottle 
filled  with  sulphuric  acid  weighs  184*3  grammes,  then  : — 

'—i-3=- 1*843,  the  specific  gravity  of  the  acid. 

Again,  the  same  bottle,  carefully  washed,  and  filled  with  rectified  spirit,  weighs  83*8  grammes, 
then  :— 

8v8 

_2_  ='838,  the  specific  gravity  of  rectified  spirit. 

100 

In  practice,  bottles  are  sold  with  perforated  stoppers,  which,  when  entirely 
filled  with  the  liquid,  and  the  stopper  dropped  in,  so  that  no  bubbles  of  air 
are  allowed  to  remain  between  the  stopper  and  the  liquid,  exactly  hold  a 
given  weight  of  water.  A  counterpoising  weight  for  the  empty  bottle  is  also 
provided ;  so  that  there  is  nothing  further  to  be  done  but  simply  to  place 
the  counterpoise  in  one  scale,  and  the  bottle,  filled  with  the  liquid  under 
examination,  in  the  other  ;  and  having  ascertained  the  weight,  to  divide  by 
the  known  weight  of  water  for  which  the  bottle  was 
constructed.  Fig.  20  shows  an  ordinary  specific-gravity 
bottle.  Fig.  21  shows  a  specific-gravity  bottle  the 
stopper  of  which  is  a  thermometer,  thus  enabling  us  to 
observe  the  exact  temperature  of  the  liquid  at  the 
moment  of  weighing. 

CASE  2.     To  take  the  specific  gravity  of  a  liquid  by 
means  of  the  hydrometer. — The  hydrometer  depends 
for  its  action  on  the  theorem  of  Archimedes.     If  a  solid 
body  be  immersed  in  a  liquid  specifically  heavier  than 
^      itself,  it  continues  to  sink  until  it  has  displaced  a  bulk 
l&     of  fluid  equal  to  its  own  weight,  and  then  it  becomes 
K  stationary.     Suppose  an  elongated  body  with  a  weight 
•^•^  at  its  base  to  cause  it  to   float   upright,   which  has  a 
specific  weight  exactly  half  that  of  water,  be  immersed 
in  that  fluid,  it  will  sink  to  exactly  half  its  length,  because  its  whole  weight  is 
counterpoised  by  a  bulk  of  fluid  equal  to  half  its  size.    A  hydrometer  is  a  long 
narrow  glass  or  metal  tube  with  a  bulb  near  the  bottom  filled  with  air,  and 
another  smaller  bulb  beneath  containing  a  sufficient  quantity  of  mercury  to 


SPECIFIC  GRAVITY.  97 

weight  it  and  cause  it  to  float  upright.  There  are  two  kinds  of  hydrometers  : 
(i)  for  fluids  heavier  than  water,  and  (2)  for  fluids  lighter  than  water.  The 
graduation  of  the  former  is  performed  by  immersing  the  instrument  in  water 
and  introducing  such  a  quantity  of  mercury  as  will  cause  it  to  sink,  so  that 
only  about  one  inch  remains  unsubmerged,  and  marking  this  point  i.  The 
instrument  is  then  plunged  successively  into  several  liquids  heavier  than 
water,  the  specific  gravities  of  which  are  known,  and  the  points  to  which 
it  rises  are  marked  and  numbered.  By  this  means  a  scale  can  be  made 
between  those  points  indicating  any  gravity  from  i  upwards.  In  hydro- 
meters for  fluids  lighter  than  water,  the  first  sinking  in  that  liquid  is  continued 
by  weighing  until  only  the  upper  bulb  is  immersed ;  and  this  point  having 
been  marked  i,  the  instrument  is  placed  successively  in  known  fluids  lighter 
than  water,  the  points  to  which  it  sinks  marked,  and  by  this  means  a  whole 
scale  is  obtained.  The  method  of  using  the  hydrometer  is  readily  Q 
seen  from  the  illustration  (fig.  22),  in  which  A  is  the  hydrometer, 
and  B  is  a  thermometer  also  placed  in  the  liquid  to  show  the 
temperature.  Most  hydrometers  being  made  to  indicate  specific 
gravity  at  15-5°  C.  (60°  F.),  it  follows  that  the  liquid  must  either 
be  first  brought  to  that  temperature  before  using  the  instrument, 
or  else  the  temperature  employed  must  be  noted,  and  a  calculation 
made,  based  upon  the  coefficient  of  expansion  of  the  liquid  in 
question. 

Syke's  hydrometer  is  used  in  England  by  the  officers  of  excise, 
to  indicate  the  strength  of  spirituous  liquors,  and  thus  facilitate  the 
collection  of  the  revenue.  It  is  a  short  brass  instrument  with  the  stem 
graduated  from  o  to  10,  and  a  series  of  nine  weights  to  place  beneath  the 
bulb.  By  observing  (i)  the  temperature,  (2)  the  wefght  put  on,  and  (3)  the 
point  to  which  it  sinks  on  the  stem,  and  referring  to  a  book  of  tables  which  is 
sold  with  the  hydrometer,  the  strength  of  the  spirit  is  ascertained.  Another 
modification  of  the  instrument  is  found  in  TwaddelFs  hydrometer,  which  is 
used  in  chemical  works  for  testing  the  density  of  liquids  having  a  greater 
specific  gravity  than  water.  It  is  so  graduated  that  the  reading  of  any  indi- 
cated degree,  multiplied  by  5  and  added  to  1000,  gives  the  specific  gravity 
as  compared  with  water.  Specific  gravity  beads  form  the  only  other  variation 
of  the  hydrometric  idea.  These  are  small  loaded  bulbs  of  known  specific 
gravities,  which  are  thrown  into  the  liquid  to  be  tested,  when  the  number 
marked  upon  the  bead,  which  just  floats  underneath  the  surface  and  shows 
no  tendency  to  sink  or  rise,  gives  the  specific  gravity  required.  Hydrometers 
in  any  form  must  in  accuracy  rank  considerably  beneath  that  of  the  specific 
gravity  bottle  ;  but  in  commercial  operations,  where  an  approximation  only  to 
correctness  is  required,  these  little  instruments  are  invaluable 

CASE  3.  To  take  the  specific  gravity  of  a  liquid  by  weighing  a  solid 
body  in  it. — Take  the  weight  of  a  glass  stopper,  or  other  suitable  plummet, 
by  suspending  it  from  the  hook  provided  for  the  purpose  in  all  balances  of 
modern  type  (see  fig.  18,  page  94).  Put  a  wooden  stool  (also  provided  with 
all  modern  balances)  over  the  pan,  and  upon  this  place  a  beaker  containing 
distilled  water  at  15-5°  C.  (60°  F.).  Let  the  plummet  hang  beneath  the  surface 
of  the  water  and  again  weigh,  and  then  empty  out  the  water,  substitute  the 
fluid  (also  at  15*5°  C.  (60°  F.)  ),  immerse  the  plummet  as  before,  and  once 
more  weigh.  By  deducting  respectively  the  weights  in  water  and  in  fluid 
from  the  weight  in  air,  we  get  the  loss  of  weight  sustained  by  the  plummet  in 
each  case.  It  is  evident  that  the  lighter  the  liquid,  the  more  the  plummet 
will  weigh  ;  therefore  we  divide  the  loss  of  weight  in  the  fluid  by  the  loss  of 
weight  in  water,  which  will  give  the  specific  gravity  of  the  liquid.  This  rule 
is  now  practically  applied  in  all  modern  laboratories  by  means  of  the  Westphal 


98        WEIGHING,  MEASURING,  AND  SPECIFIC  GRA  VITY. 


balance  (fig.  23).  By  this  a  small  thermometer  (A),  adjusted  to  a  counter- 
balancing weight  (B),  is  placed  in  the  liquid,  and  the  loss  of  weight  is  restored 
by  little  rider  weights  placed  on  the  beam,  which  are  so  contrived  as  to  readily 
indicate  the  specific  gravity  without  calculation. 

(B}  Specific  Gravity  of  Solids. 

CASE  i.  To  take  the  specific  gravity  of  a  solid  body  in  mass  which  is 
insoluble  in  and  heavier  than  water. — The  method 
by  which  this  process  is  conducted  was  suggested  by 
a  theorem  attributed  to  Archimedes,  which  may  be 
thus  expressed: — A  solid  on  being  immersed  in  a 
liquid  is  buoyed  up  in  proportion  to  the  weight  of 
the  fluid  which  it  displaces,  and  the  weight  it  thus 
apparently  loses  is  equal  to  that  of  its  own  bulk  of 
the  liquid.  A  piece  of  the  solid  substance  to  be  tested 
is  weighed,  and  is  suspended  by  means  of  a  fine 
thread  from  one  arm  of  a  balance  so  that  it  dips 
under  the  surface  of  a  vessel  containing  distilled  water 


<n"  —  rr  "y 

T 

•o      n.            -.._ 

in 

1 

U  J 

Fig.  a3. 


at  15*5°  C.  (60°  F.),  when  its  weight  is  again  noted. 


Its  weight  in  water  is  deducted  from  its  weight  in  air,  and  the  weight  in  air 
is  divided  by  the  difference  so  obtained,  which  gives  the  specific  gravity. 


EXAMPLE. 

A  piece  of  marble  weighs 
Immersed  in  distilled  water    . 


30       grammes. 
18-89         » 


Difference  in  weight irn         ,, 

By  dividing  30  by  ii'ii  we  obtain  the  quotient  27,  which  is  the  specific  gravity  of  the 
marble.  The  practical  arrangement  has  been  already  described  above  (Liquids,  Case  3). 

CASE  2.  To  arrive  at  the  specific  gravity  of  a  powder  which  is  insoluble 
in  and  heavier  than  water.— Weigh  a  portion  of  the  powder  in  air,  then 
introduce  it  into  a  counterpoised  specific  gravity  bottle  constructed  to  hold 
a  known  weight  of  water.  Let  the  bottle  be  carefully  filled  with  distilled 
water,  gently  agitating  to  insure  that  no  minute  bubbles  of  air  shall  remain 
attached  to  the  particles  of  powder  ;  then  weigh  the  whole.  From  the  \veight 
of  the  powder  in  air,  plus  the  known  weight  of  water  which  the  bottle  should 
contain,  deduct  the  weight  obtained  in  the  second  operation,  and  divide  the 
original  weight  of  the  powder  by  this  difference. 

EXAMPLE. — 2  grammes  of  a  powder  are  weighed  out,  and  poured  into  a  counterpoised 
specific  gravity  bottle,  constructed  to  hold  100  grammes  of  water.  The  bottle  thus  charged 
is  found  to  weigh  ioi'2  grammes  ;  then — 


2  grammes  -»- 100  grammes  =      102    grammes. 

Weight  of  the  bottle  when  charged  ) 

with  powder  and  water       .         .  f  " 

Difference 


Difference '8        „ 

Therefore,  2  grammes  divided  by  '8  gramme  will  give  2 '5  as  the  specific  gravity  of  the 
powder. 

CASE  3.  To  take  the  specific  gravity  of  a  substance  in  mass,  insoluble  in, 
but  lighter  than,  water. — The  difficulty  met  with  m  this  case  consists  in  the 
impossibility  of  weighing  such  a  substance  alone  in  water,  because  it  floats  on 
the  surface  of  that  liquid.  It  therefore  becomes  necessary  to  attach  a  piece 
of  lead  sufficiently  heavy  to  sink  it,  and  thus  a  complication  is  introduced. 
The  light  substance  is  first  weighed  in  air  in  the  ordinary  manner,  and  is  then 
attached  to  a  sinker,  and  suspended  from  one  arm  of  a  balance  under  the 
"urface  of  distilled  water,  when  the  combined  weight  of  both  is  ascertained. 


SPECIFIC  GRAVITY.  99 


The  light  body  is  now  detached,  and  the  weight  of  the  sinker  alone  in  water 
noted.  By  these  means  we  obtain  the  following  data  : — 

i.  The  weight  of  the  light  body  in  air. 
ii.  The  weight  of  the  sinker  in  water, 
iii.  The  weight  conjointly  of  the  light  body  and  sinker  in  water. 

We  then  deduct  the  weight  of  both  in  water  from  the  weight  of  the  sinker  ir 
water ;  add  the  weight  of  the  light  substance  in  air ;  and  divide  the  weight  of 
the  light  body  in  air  by  the  product  so  obtained. 

EXAMPLE. — A  light  substance  weighs  12  grammes  in  air  ;  being  attached  to  a  piece  of  lead 
and  weighed  in  distilled  water  the  united  weight  amounts  to  4  grammes,  while  the  weight  of 
the  lead  alone  in  water  shows  5  grammes.  Then  : — 

Weight  of  lead  in  water        ...         5  grammes. 
Weight  of  both  in  water  .         .        4        ,, 

Difference I  gramme. 

Add  weight  of  light  body  in  air     .         .       12  grammes. 

Sum      ....  13        ,, 

Dividing  12,  the  weight  in  air,  by  13  obtained  as  above,  we  arrive  at  the  decimal  fraction 
•923  as  the  specific  gravity  of  the  light  substance  tested. 

CASE  4.  To  obtain  the  specific  gravity  of  a  substance  soluble  in  water. — 
Proceed  exactly  in  the  same  manner  as  in  Case  2  or  3,  according  as  the  body 
is  in  mass  or  in  powder ;  but  instead  of  water,  use  oil  of  turpentine  or  some 
other  liquid  in  which  the  solid  is  insoluble.  Having  obtained  the  specific 
gravity  of  the  substance  by  calculating  just  as  if  water  had  been  used,  multiply 
the  result  by  the  known  specific  gravity  of  the  oil  of  turpentine  or  other  fluid 
employed. 

EXAMPLE. — A  lump  of  sugar  weighing  10  grammes  was  found  to  weigh  when  immersed  in 
oil  of  turpentine  4*562  grammes.  Then — 

The  weight  of  the  sugar  in  air  was  10          grammes. 

,,  ,,  oil  of  turpentine  4  '562          ,, 

Difference    .  ...  .         5 '438          ,, 

Dividing  10  grammes  by  5*438  grammes  yields  1*84  as  the  specific  gravity,  as  if  water  had 
been  used  ;  and  by  multiplying  this  result  by  '87,  the  specific  gravity  of  oil  of  turpentine,  we 
obtain  I  *6  as  the  actual  specific  gravity  of  the  sample  of  sugar  operated  on. 

Having  thus  considered  in  detail  the  various  complications  which  may  arise 
in  taking  the  specific  gravity  of  liquids  and  solids,  it  only  remains  to  point  out 
how  the  foregoing  may  be  rendered  subservient  to  commercial  purposes. 

(C)  Practical  Applications  of  Specific  Gravity  of  Solids  and  Liquids. 

CASE  i.  The  specific  gravity  of  a  body  being  known,  it  is  desired  to  as 
certain  the  weight  of  any  given  volume  of  the  substance.  Find  the  weight 
of  the  given  bulk  considered  as  water,  and  multiply  this  amount  by  the 
specific  gravity. 

EXAMPLE  i.— What  would  be  the  weight  of  a  fluid  ounce  of  oil  of  vitriol  ?  We  know  that 
a  fluid  ounce  of  distilled  water  weighs  437*5  grains,  and  the  specific  gravity  of  oil  of  vitriol  is 
1-843  >  so>  if  we  multiply  the  former  figures  by  the  latter,  we  obtain  806 '31  grains,  which  is 
the  weight  of  a  fluid  ounce  of  this  acid. 

EXAMPLE  ii. — How  much  should  a  litre  of  chloroform  weigh?  The  weight  of  a  litre  of 
water  is  1000  grammes  ;  and  by  multiplying  1000  by  i  -49,  the  specific  gravity  of  the  chloroform, 
we  obtain  1490  grammes,  as  an  answer  to  the  question. 

EXAMPLE  iii.  —  How  much  should  a  fluid  ounce  of  pure  ether  weigh?  The  specific  gravity 
is  72,  and  a  fluid  ounce  of  distilled  water  weighs  437*5  grains  ;  multiplying  the  one  number 
by  the  other  gives  315  grains. 


ioo      WEIGHING,  MEASURING,  AND  SPECIFIC  GRA  VITY. 

CASE  2.  Given  the  weight  of  any  known  bulk  of  a  liquid,  to  find  its 
specific  gravity.  —  Divide  the  weight  by  that  of  the  given  bulk  considered  as 
distilled  water. 

EXAMPLE.  —  A  pint  of  spirit  weighs  16}  ounces.  Is  it  rectified  or  proof  spirit  ?  By  dividing 
this  weight  by  20  ounces,  the  ascertained  weight  of  a  pint  of  distilled  water,  we  obtain  as  an 
answer  '838.  We  know,  therefore,  that  the  spirit  thus  tested  must  have  been  rectified. 

CASE  3.  To  find  the  amount  of  solid  matter,  in  grammes,  present  in  100  c.c. 
of  a  solution  of  given  specific  gravity.  So  far  as  any  ordinary  rule  can  be 
laid  down,  especially  with  regard  to  saccharine  liquids,  for  which  this  calcula- 
tion is  generally  used,  we  multiply  the  gravity  by  1000,  and  then,  having 
deducted  1000  from  the  product,  we  divide  by  3  '85. 

EXAMPLE.  —  A  saccharine  solution  has  a  gravity  of  i'OU4  :  how  much  solid  matter  in 
grammes  does  it  contain  in  each  c.c.  ? 

i'oii4X  looo  =  1011*4  —  IODO  =  ii'4  .*.  —  ^=  2*961  grammes  per  loo  c.c. 

3  "o5 

(D)  Specific  Gravity  of  Gases. 

Taking  the  density  of  gases  and  vapours  involves  many  more  complicated 
considerations  than  are  required  in  the  methods  applicable  to  the  specific 
gravity  of  liquids  and  solids.  The  standard  adopted  for  such  bodies  is 
hydrogen,  measured  at  a  temperature  of  o°  C.  and  a  barometrical  pressure 
of  760  millimetres  (N.T.P.). 

When  taking  the  specific  gravity  of  liquids  or  solids,  it  is  easy  to  obtain  the 
water  or  other  fluid  required  at  the  exact  temperature  necessary,  by  the  use  of 
cooling  or  heating  appliances.  With  a  gas  we  need  exercise  no  such  manipu- 
lation, because  the  coefficient  of  expansion  of  all  vapours  and  gases  is  alike 
and  well  ascertained.  The  measurement  of  gases  is  therefore  conducted 
without  any  attempt  to  modify  these  conditions  ;  but  the  indication  of  the 
thermometer  and  barometer  being  carefully  noted  at  the  time  of  the  experi- 
ment, a  simple  series  of  calculations  enables  us  to  ascertain  how  much  the 
volume  of  gas  would  have  measured  had  the  test  been  conducted  at  a  standard 
of  temperature  and  pressure.  The  following  are  specimens  of  such  calcu- 
lations :  — 

Correction  of  the  volume  of  a  gas  for  changes  of  temperature.  —  This  is 
based  on  Charles'  law,  which  states  that  "  the  volume  occupied  by  any  given 
weight  of  a  gas  is  directly  proportional  to  its  absolute  temperature."  Absolute 
temperature  means  degrees  above  273°  C.,  which  is  the  absolute  zero  of  tem- 
perature. To  convert  degrees  of  ordinary  temperature  into  absolute  degrees, 
it  is  therefore  necessary  to  add  273  to  all  degrees  above  zero,  while  degrees 
below  o°  are  to  be  deducted  from  273.  From  this  law,  given  —  v,  the  volume  ; 
v,  the  required  volume  ;  /,  the  given  absolute  temperature  ;  and  /*,  the  required 
absolute  temperature  ;  —  we  employ  the  following  calculations  :  — 


Correction  of  the  volume  of  a  gas  for  changes  of  pressure.  —  The  law  of 
Boyle  states  that  "the  volume  occupied  by  any  given  weight  of  a  gas  is 
inversely  proportional  to  the  pressure."  Therefore,  /  being  the  given  pressure, 
and/'  the  required  pressure,  we  have  — 


When  a  gas  is  measured  it  is  generally  necessary  to  correct  for  both  con- 
ditions, and  then  we  employ  double  proportion.  Vhe  following  formulae  will 
be  found  useful  as  meeting  all  ordinary  cases  :— 


SPECIFIC  GRAVITY.  101 


(1)  Wanted  the  change  of  volume  resulting  from  a  given  alteration  of 

temperature  and  pressure : — 

p  x  f  x  v  _   , 

p'xt 

(2)  Wanted  the  change  of  temperature  resulting  from  a  given  alteration 

of  volume  and  pressure  : — 

/  x  if  x  /  _  f 
px  v 

(3)  Wanted  the  change  of  pressure  resulting  from  a  given  alteration  of 

volume  and  temperature  : — 

x  f  x 


=  /• 
v*  x  / 

(4)  To  find  the  volume  at  N.T.P.  of  any  gas  measured  at  a  given 
temperature  and  pressure  (the  temperature  being  above  o°) : — 

/  x  273  x  v  _, 


P  X  (273  +  given  temp.) 

Or,  in  a  decimal  fraction  (dt  =  difference  between  o°  and  given 

temperature) : — 

/  x  (i  +  -003665  dt)  ~ 

The  manner  in  which  the  specific  gravity  of  a  permanent  gas  was  formerly 
obtained  was  by  exhausting  a  thin  glass  globe  by  means  of  the  air-pump  and 
weighing  it ;  then  filling  it  with  air  at  known  temperature  and  pressure,  and 
weighing  ;  and  lastly,  pumping  out  the  air,  filling  the  globe  with  the  gas  at  a 
similar  temperature  and  pressure,  and  again  weighing.  After  deducting  the 
weight  of  the  empty  globe  from  each  of  the  two  latter  weights,  the  weight  of 
the  gas  was  divided  by  that  of  the  air. 

Now,  however,  in  modern  laboratories  all  that  is  practically  done  away  with, 
and  the  standard  taken  for  the  density  of  gases  and  vapours  is  hydrogen ; 
because  (i)  it  is  the  lightest  known  gas,  and  (2)  we  know  the  weight  of  any 
given  volume  of  it  without  the  necessity  of  weighing  each  time.  Therefore, 
to  take  the  density  of  a  gas  or  vapour  we  weigh  a  given  number  of  cubic 
centimetres  of  the  gas,  noting  the  temperature  and  pressure  at  the  moment 
of  weighing,  and  having  corrected  the  volume  so  obtained  to  N.T.P.,  we 
divide  this  by  the  weight  of  the  same  number  of  c.c.  of  hydrogen.  A  litre  of 
hydrogen  at  o°  C.  and  760  mm.  bar.  weighs  "0896  gramme;  therefore  each 
c.c.  of  H  will  weigh  "0000896  gramme. 

(E)  Vapour  Density. 

After  finding  the  percentage  composition  of  substances  by  analysis,  and 
from  that  calculating  an  empirical  formula  (which  is  done  by  dividing  the 
percentage  of  each  element  by  its  own  atomic  weight,  then,  taking  the  lowest 
of  these  answers  as  unity,  dividing  all  the  others  by  it  and  expressing  the 
mutual  ratios  in  the  simplest  full  numbers),  it  is  necessary  to  prove  whether 
the  sum  of  such  formula  is  the  true  molecular  weight.  Upon  the  theory  that 
all  molecules  occupy  a  space  double  that  of  an  atom  of  hydrogen,  we  can 
prove  our  case  by  taking  the  hydrogen  density  of  the  substance  in  vapour  (if 
volatile),  and  then  such  vapour  density  x  2  =  the  true  molecular  weight. 
This  research  acts  as  a  check  upon  our  formula  obtained  by  analysis,  and 
may  or  may  not  lead  to  our  having  to  multiply  it  until  its  sum  equals  th« 
required  weight  thus  found. 


102      WEIGHING,  MEASURING,  AND  SPECIFIC  GRA  VITY. 

(a)  Meyer's  Method. — This  is  the  simplest  and  most  rapid  process.     The 
apparatus  used  is  illustrated  in  fig  24.     The  inner  tube  (A)  is  closed  with 
a  cork  and  arranged  so  that  its   bent  delivery  tube   just   dips   under  the 
surface  of  mercury  contained  in  a  trough.     Any  suitable  liquid,  boiling  at  a 
higher  temperature  than  the  body  of  which  the  density  is  to  be  taken,  is 
placed  in  the  outer  tube  (B),  and  heat  being  applied  so  as  to  boil  the  fluid, 

the  air  in  the  inner  tube  expands  and  passes  off  through  the  mercury. 
When  bubbles  of  air  cease  to  pass,  some  water  is  poured  upon  the 
surface  of  the  mercury,  and  a  graduated  gas  collecting  tube,  filled 
with  water,  is  inverted  over  the  delivery  tube.     A  known  weight  of 
the  substance,  enclosed  in  a  specially  made  minute  stoppered  bottle, 
is  then  introduced  into  the  inner  tube  (A)  by  rapidly  raising  the  cork, 
dropping  the  bottle  in,  and  instantly  closing.     The  vapour  produced 
now  displaces  an  equivalent  volume  of  air,  which  passes  into  the 
measuring  tube.     When  action  ceases,  the  cork  is  opened  to  prevent 
back  suction,  and  the  air  in  the  tube  is  measured,  noting  tempera- 
ture and  pressure.     This  volume  in  c.c.  when  corrected  to  N.T.P., 
and  multiplied  by  '0000896,  gives  the  weight  of  a  volume  of  hydrogen 
equal  to  that  of  the  vapour,  and  lastly,  by  dividing  the  weight  of  the 
substance  taken,  by  this  calculated  weight,   we  obtain  the  vapour 
density.     The  coefficient  of  expansion  of  all  gases  being  practically 
Fig.  24.     equal,  it  is  evidently  the  same  thing  whether  we  measure  a  volume 
of  actual  vapour  at  a  given  temperature,  or  that  of  an  equivalent 
volume  of  air  displaced   by  it  at   the  same   temperature.     Such   a  minute 
quantity  of  the  substance  must  be  taken  as  shall  not,  when  in  vapour,  more 
than  displace  the  air  contained  in  the  inner  tube  of  the  apparatus  (which 
should  hold  about  100  c.c.),  otherwise  the  whole  process  manifestly  fails.     As 
the  gas  is  collected  over  water  it  is  necessary  to  refer  to  a  table  of  the  tension 
of  aqueous  vapour  at  the  temperature  of  measuring,  and  to  deduct  it  from  the 
observed  height  of  the  barometer,  before  correcting  to  N.T.P. 

(b)  Dumas'  Process. — A  thin,  clean,  dry  glass  globe,  about  three  inches  in 
diameter,  is  employed.     Its  neck  having  been  drawn  out  to  a  fine  tube  in  the 
blowpipe  flame,  it  is  weighed,  and  the  temperature  and  pressure  noted.     By 
gently  heating  the  bulb  and  dipping  the  open  end  into  the  volatile  liquid,  a 
suitable  quantity  is  drawn  into   the   globe    by  the    contraction   of  the   air. 
Attaching  a  handle  by  means  of  wire,  the  sphere  is  plunged  into  an  oil  bath 
furnished  with  a  thermometer,  and  is  then  heated  somewhat  above  the  volati- 
lising point  of  the  contained  liquid.     When  all  vapour  has  ceased  to  issue 
from  the  globe,  the  orifice  is  hermetically  sealed,  and  the  temperature  and 
pressure  again  noted.      The   apparatus  is  allowed  to  cool,  separated  from 
the   handle,  cleansed,  weighed,   and   the  weight   noted.      The   last  step  is 
to  break  off  a  fragment  of  the  neck  beneath  the  surface  of  a  sufficiency  of 
mercury,  when,  should  the  experiment  have  been  carefully  performed,  the 
liquid  enters  the  globe,  completely  filling  it,  and  the  capacity  is  ascertained 
by  emptying  its  contents  into  a  graduated  glass  measure.      Supposing  the 
experiment  to  have  been  perfectly  successful,  we   have   the   following   five 
data : — 

1.  Weight  of  globe  filled  with  air. 

2.  Temperature  and  pressure  at  the  time  of  weighing. 

3.  \Veight  of  globe  plus  vapour. 

4.  Temperature  and  pressure  at  sealing. 

5.  Capacity  of  the  globe. 

Proceeding  from  these  data,  the  first  point  is  to  find  the  actual  weight  of 
the  globe.     This  is  done  by  calculating  the  capacity  of  the  globe  from  the 


SPECIFIC  GRAVITY.  103 


temperature  and  pressure  at  the  time  of  weighing  to  o°  C.  and  760  mm.  bar., 
and  then  multiplying  the  true  volume  thus  found  by  '001295,  which  is  the 
weight  of  a  cubic  centimeter  of  air  (i  litre  at  o°  C.  and  760  mm.  bar.  =•  1*295 
gramme).  Having  thus  obtained  the  weight  of  the  air,  it  is  deducted  from 
the  weight  of  globe  and  air,  and  the  difference  gives  the  true  weight  of  the 
globe ;  and  by  deducting  this  latter  from  the  weight  of  the  globe  plus  vapour, 
we  obtain  the  actual  weight  of  the  vapour.  But  as  this  weight  is  that  of  the 
volume  of  vapour  at  the  temperature  and  pressure  at  the  moment  of  sealing, 
it  must  be  corrected  to  standard  temperature  and  pressure,  and  the  weight  of 
an  equal  volume  of  hydrogen  ascertained.  To  do  this,  the  capacity  of  the 
globe  is  once  more  put  down,  and  reduced  from  the  temperature  and  pressure 
at  sealing  to  o°  C.  and  760  mm.  bar.,  and  the  resulting  volume  is  multiplied 
by  "0000896,  which  is  the  weight  of  i  cubic  centimeter  of  hydrogen.  The 
product,  which  gives  the  actual  weight  of  an  equivalent  volume  of  hydrogen, 
is  then  taken,  and  divided  into  the  weight  of  the  vapour  already  found,  and 
the  answer  is  the  density. 


(F)  Note  on  TJ.S.P,  "Weights,  Measures,  and  Specific  Gravities, 

The  American  Pharmacopoeia  has  entirely  discontinued  the  use  of  any 
weights  and  measures  except  those  of  the  metrical  system,  viz  : — 

gramme  to  gram,  abbreviated  to  Gm. 

litre  to  liter  ,,  ,,  lit.  or  1000  Cc. 

cubic  centimetre  to  cubic  centimeter,  abbreviated  to  Cc. 

These  abbreviations,  being  very  convenient,  will  be  employed  in  the  following 
chapter  on  Volumetric  Analysis. 

Owing  to  the  fact  that  the  average  temperature  of  laboratories  in  the 
U.S.A.  is  nearer  25°  C.  (77°  F.)  than  15-5°  C.  (60°  F.),  the  Committee  of 
Revision  of  the  U.S. P.  have  decided  upon  the  former  temperature  as  the 
working  standard.  All  the  specific  gravities  given  in  Chapter  XL  of  this 
book  have  been  revised  in  accordance  with  this  decision,  and  are  all 
supposed  to  be  taken  at  25°  C.  as  against  an  equal  volume  of  water  also 
at  25° C. 


CHAPTER   VII. 

VOLUMETRIC    QUANTITATIVE    ANALYSIS. 


I.  INTRODUCTORY    REMARKS. 

VOLUMETRIC  analysis  is  that  in  which  the  quantity  of  any  reagent  required  to 
perform  a  given  reaction  is  ascertained,  and  the  amount  of  the  substance  acted 
upon  is  found  by  calculation.  The  process  of  adding  the  reagent  from  a 
graduated  measure  is  called  titration. 

(A)  Volumetric  or  standard  solution  is  a  solution  of  definite  strength,  made 
by  dissolving  a  given  weight  of  a  reagent  in  grams  in  a  definite  volume  of 
water  in  cubic  centimeters.  Such  solutions  are  usually  made  on  the  following 
principles  : — 

The  theoretical  normal  solution  is  an  imaginary  one,  containing  i  Gm.  of 
hydrogen  in  i  liter  (1000  Cc.)  of  water,  and  a  normal  solution  of  any  reagent 
is  such  a  weight  of  the  substance  in  Gm.  (also  i  liter  of  water)  as  is 
capable  of  combining  with,  displacing,  or  otherwise  performing  a  chemical 
function  equal  to  that  of  i  Gm.  of  hydrogen.  This  weight  is  termed  the 
equivalent  of  the  reagent,  and  it  is  ascertained  as  follows  :— 

(a)  Trie  reagent  is  an  element.  We  divide  the  atomic  weight  of  the 
element  by  its  valency.  Thus — 

H'  =  i,  Cl'  =  35-5,  Br'  =  80,  I'  -  127,  O"  -  8,  etc. 

(^)  The  reagent  is  an  acid  or  an  alkali.  We  divide  the  molecular 
weight  by  the  active  combining  power,  as  shown  by  the  number 
of  atoms  of  displaceable  hydrogen  in  acids,  and  by  the  valency 
of  the  base  in  alkalies  : — 

Name.  Formula.  Equivalent. 

Hydrogen          .  H  =      i 

Hydrochloric  acid  HC1  =   36 -37 

Sulphuric  acid  .  H2SO4H-2  =48-91 


Citric  acid 


Sodium  hydroxide 
Calcium  hydroxide 
Potassium  carbonate 
Potassium  bicarbonate 


H,C6H40,H20-r3  -  69-83 


NallO  =  39-96 

Ca(HO)2-r-2  =  56-87 

K,CO3— 2  -  68-95 

KHCO3  =  99-88 

(c]  The  reaction  is  a  special  one,  depending  on  a  particular  action.  We 
divide  the  molecular  (or  atomic)  weight  of  the  reagent  by  its 
combining  power,  as  shown  in  the  equation.  For  example, 
taking  the  case  of  the  action  between  iodine  and  arsenious 
acid,  we  find  the  equation  : — 

As2O3  +  2l2  +  2H2O  =  As2O5  +  4HI. 

Each  atom  of  iodine  being  equivalent  of  one  of  hydrogen,  it 
follows  that  each  H  would  equal  \  of  As2Os ;  therefore  a  normal 
solution  of  that  body  would  be  198  -f-  4  =  49-5  Gm.  per  liter, 
and  would  exactly  decolorize  i  atomic  weight  (=127  Gm.)  of 
iodine. 

104 


INTRODUCTORY  REMARKS.  105 

The  following  abbreviations  are  used  to  express  the  strength  of  standard 
solutions : — 

N    =  a  normal  solution  having  I  equivalent  weight  in  Gm.  per  1000  Cc. 
^     =  a  half-normal  solution  having  ^  equivalent  weight  in  Gm.  per  1000  Cc. 
yjj-  =  a  tenth-normal  solution  having  ^  equivalent  weight  in  Gm.  per  1000  Cc. 
£Q  =  a  fiftieth-normal          „  -fa          „  „          ,,  ,, 

(^)  An  indicator  is  a  substance  added  to  enable  us  to  ascertain,  by  a 
change  of  color  (or  other  equally  marked  effect),  the  exact  point  at  which 
a  given  reaction  is  complete. 

The  principal  indicators  employed  are  prepared  as  follows  : — 

(1)  Indicators  for  estimating  acids  or  alkalies. 

(a)  Litmus  indicator.  Boil  powdered  litmus  in  alcohol  of  '82  sp.  gr. 
repeatedly  till  no  more  red  color  is  extracted,  and  then  digest 
the  residue  in  an  equal  weight  of  cold  distilled  water.  Pour  or 
filter  off,  and  then  boil  the  blue  powder  remaining  in  5  times 
its  weight  of  distilled  water ;  filter  and  preserve  the  filtrate  in 
a  bottle  stoppered  with  a  loose  plug  of  cotton,  so  that  air 
is  admitted,  but  dust  excluded.  This  indicator  is  blue  with 
alkalies  and  red  with  acids,  and  is  affected  by  all  acids,  includ- 
ing CO2.  It  therefore  does  not  give  a  reliable  indication 
with  alkaline  carbonates  unless  the  CO2  is  expelled  by  boiling. 

(b}  Phenol-phthalein  indicator.  Make  a  i  per  cent,  solution  of  phenol- 
phthalein  in  diluted  alcohol  of  '937  sp.  gr.,  i.e.  i  Gm.  in 
100  Cc.  This  solution  is  red  with  alkalies,  and  colorless  with 
acids.  It  is  not  suitable  as  an  indicator  with  ammonia  or 
alkaline  bicarbonates. 

(c)  Methyl-orange  indicator.  Dissolve  i  Gm.  of  methyl  orange  (or  the 
commercial  dyes  known  as  helianthin,  Palmer's  orange  jP  or 
tropceolin  D)  in  1000  Cc.  of  distilled  water.  Into  this  carefully 
drop  diluted  sulphuric  acid  till  the  liquid  turns  red  and  just 
ceases  to  be  transparent,  and  then  filter.  This  solution  is 
yellow  with  alkalies  and  red  with  mineral  acids,  but  is  not 
affected  by  CO2  or  boric  acid,  so  that  it  is  the  best  indicator 
for  the  analysis  of  alkaline  carbonates  and  borax.  It  cannot, 
however,  be  used  with  oxalic  acid  or  organic  acids  generally. 

(d}  Cochineal,  Hematoxylin  and  lodeosin  indicators.  These  solutions 
are  specially  employed  as  indicators  for  the  titration  of  alka- 
loids. Full  instructions  for  their  preparation  will  be  found  in 
Chapter  XL  when  treating  of  the  assay  of  alkaloidal  drugs. 

Note.  —  The  U.S. P.  gives  a  very  suitable  warning  as  to  the  above  indicators,  which  is 
worthy  of  being  quoted  in  full.  It  says:  "  Each  test-solution  used  as  indicator  should  be 
examined  as  soon  as  prepared,  and  afterwards  from  time  to  time,  as  to  its  neutrality.  If 
necessary,  it  should  be  brought,  by  the  cautious  addition  of  diluted  sulphuric  acid,  or  of  a  dilute 
solution  of  an  alkali,  to  such  a  point  that,  when  a  few  drops  of  it  are  added  to  25  Cc.  of 
water,  a  single  drop  of  a  centinormal  acid  or  alkali,  respectively,  will  distinctly  develop  the 
corresponding  tints.  Since  many  of  the  colored  test-solutions  are  injured  by  exposure  to 
light,  it  is  best  to  preserve  them  in  dark  amber-colored  vials." 

(2)  Indicators  for  special  purposes 

(a)  Starch  mucilage.  Mix  i  Gm.  of  starch  (arrowroot  is  preferable) 
with  10  Cc.  of  cold  water,  and  then  add  enough  boiling  water, 
with  constant  stirring,  to  make  about  200  Cc.  of  a  thin, 


io6 


VOLUMETRIC  QUANTITATIVE  ANALYSIS. 


transparent  jelly.  To  preserve  this  solution  for  any  length  of 
time,  10  Gm.  of  zinc  chloride  should  be  added  to  it,  and  the 
solution  transferred  to  small  bottles,  which  should  be  well 
stoppered.  It  is  used  for  the  detection  of  free  iodine,  with 
which  it  strikes  a  dark  blue. 

(b]  Potassium  chromate  solution.     Dissolve   10  Gm.  of  pure  K2CrO4 

in  TOO  Cc.  of  water,  then  carefully  drop  in  dilute  solution  of 
argentic  nitrate  till  a  slight  red  turbidity  is  produced,  let  settle, 
and  pour  off  into  a  stoppered  bottle.  This  solution  gives  a  red 
precipitate  with  AgNOs,  but  not  until  any  chloride,  bromide, 
iodide,  or  cyanide  present  has  entirely  combined  with  the  silver. 

(c)  Potassium  ferricyanide  solution.       Dissolve    i    part  of  potassium 

ferricyanide  in  about  10  parts  of  water.  This  solution  must 
be  made  freshly  when  required,  as  it  is  rapidly  decomposed 
by  light.  The  freshly  prepared  aqueous  solution,  when  mixed 
with  some  ferric  chloride  solution  and  diluted  with  water,  must 
show  a  brown  tint,  free  from  turbidity  or  any  shade  of  green. 

(C)  The  apparatus  specially  employed  in  volumetric  analysis. 

i.  The  measuring  flask,  so  constructed  as  to  hold  a  definite  amount  of 
fluid  (say  1000  or  100  Cc.)  when  filled  up  to  the  mark  on  the 
neck  (fig.  25). 

-I 


Fig.  25.  Fig.  26.  Fig.  27.  Fig.  28. 

2.  The  test  mixer,  a  cylindrical  vessel,  to  hold  i  liter  of  fluid  graduated 

in  measures  of  10  Cc.  each  (fig.  26). 

3.  The   burette,   a   graduated  tube,    usually   containing    100  Cc.  and 

graduated  in  divisions  of  i  Cc.  (or  50  Cc.  in  -^  Cc.),  for  con- 
taining and  delivering  the  standard  solution.  This  is  fitted 
with  a  clamp  or  stopcock  at  the  bottom,  which,  when  pressed 
or  turned,  allows  the  contained  liquid  to  run  out  at  any 
regulated  speed  desired.  It  should  also  be  furnished  with  an 
appliance  called  "  Erdmann's  float,"  which  enables  us  to  read 
the  quantity  of  fluid  delivered  more  accurately.  (Fig.  27 
shows  two  burettes  in  their  stand  as  usually  employed.) 

4.  The  pipette  is  an  instrument  graduated  to  deliver  a  fixed  volume  of 

liquid  (say  10,  20,  50,  or  100  Cc.).  Fig.  28  shows  a  set  of  such 
instruments  arranged  in  a  convenient  stand. 


INTRODUCTORY  REMARKS.  107 

(D)  Weighing  operations.     The  student  should  have  a  tared  watch-glass 
for  weighing  out  solids  and  a  small  stoppered  bottle  for  weighing  volatile 
liquids.     By  carefully  keeping  these  much  trouble  is  saved. 

(1)  To  weigh  a  solid.     Place  the  tared  glass  on  the  scale,  and  put  on 

it  what  is  judged  to  be  a  sufficient  quantity  of  the  article  to  be 
weighed,  then  weigh  the  whole  and  note  the  weight  thus  : — 

Glass  +  substance 5*632  Gm. 

Known  tare  of  glass         ....     5-132     ,, 

Weight  taken  for  analysis        .         .         .       -500     ,, 

(2)  To  weigh  a  volatile  liquid.    Fill  the  small  stoppered  bottle  with  the 

liquid  and  weigh ;  pour  out  what  is  judged  to  be  sufficient  into 
the  flask  containing  the  indicator,  replace  the  stopper  and  again 
weigh,  noting  each  weight  at  the  time  thus  : — 

Total  weight  of  bottle  +  fluid  .         .         .     20-982  Gm. 
Weight  of  bottle  +  fluid  after  pouring  out     15-482     ,, 

Weight  of  fluid  taken        ....       5'5oo     ,, 

Note. — It  is  most  important  always  to  take  the  weights  directly  down  in  a  note-book 
from  the  balance,  and  to  cultivate  the  habit  of  always  replacing  the  weights 
in  tJieir  proper  holes  in  the  weight  box  when  finished.  This  enables  us  to 
have  a  double  check — (i)  from  the  weights  in  the  pans,  and  (2)  from  looking 
at  the  empty  holes  in  the  weight  box,  In  weighing  brass  weights  are  used 
from  50  to  I  Gm.  ;  flat  platinum  weights  from  "5  to  "Oi  Gm.  ;  and  the  rider 
on  the  beam  is  used  for  milligrams  (i.e.  -009  to  -ooi).  Before  weighing, 
see  that  all  the  weights  are  in  their  right  places  in  the  box.  At  the  conclu- 
sion of  the  weighing,  read  off  the  weights  and  put  them  down  in  a  note-book, 
and  then  check  that  reading  by  putting  them  back  into  the  box,  looking,  as 
you  do  so,  at  the  note  already  made.  Always  close  the  case  of  the  balance 
before  using  the  rider,  so  as  to  prevent  currents  of  air  affecting  the  weight. 

(E)  General  modus  operandi.     A  known  weight  of  the  substance  to  be 
analyzed  is  accurately  weighed,  and,  having  been  placed  in  a  flask,  and  dissolved 
in,  or  diluted  with,  water  (if  necessary),  the  indicator  is  added,  and  the  standard 
solution  of  the  reagent  is  dropped  in  from  a  burette  until  the  desired  effect  is 
produced.     The  number  of  Cc.  of  standard  solution  used  having  been  noted, 
it  is  multiplied  by  the  "  Cc.  equivalent "  of  the  substance  analyzed. 

Suppose,  for  example,  we  desire  to  ascertain  the  purity  of  a  sample  of 
sodium  hydroxide,  and,  having  weighed  out  i  Gm.,  we  find  that  24  Cc.  of 
standard  normal  oxalic  acid  were  required  for  exact  neutralization.  Normal 
oxalic  acid  is  62*85  Gm.  per  liter,  or  '06285  in  each  Cc.,  and  by  the  equation 
we  find — 

H2C2O4 .  2H2O  +  2NaHO  -  Na,C2O4  +  4H2O. 

2)1257  2)79-92 

62-85  39'9^  -  39-96  Gm.  of  NaHO,  equivalent  to  62-85  Gm.  acid. 

The  normal  liter  equivalent  of  NaHO  is  therefore  39*96,  and  the  normal  Cc. 
equivalent  is  39*96  -*-  1000  =  '03996 ;  therefore  each  Cc.  of  acid  used  will 
represent  '03996  Gm.  of  soda.  Then — 

24  X  -03996  =  -95904  Gm.  of  real  NaHO  in  the  I  Gm.  weighed  out  for  analysis. 
Lastly— 

—  =  95  '9°4  Per  cent-  real  soda  in  sample. 

Expressing  the  above  in  rules  to  commit  to  memory,  we  have  the  follow- 
ing steps  :— 

I.  Write  out  the  equation  and  reduce  the  first  side  of  it  to  normal 
equivalent  weights. 


io8  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

II.  According  to  the  strength  of  the  standard  solution  employed, 
divide  the  normal  equivalent  of  the  substance  under  analysis 
by  1000  (for  normal  solution),  10,000  (for  decinormal),  etc., 
thus  getting  the  "  Cc.  equivalent." 

III.  Multiply  the  number  of  Cc.  of  standard  solution  used  from  the 
burette  by  the  Cc.  equivalent  of  the  substance  analyzed,  thus 
getting  the  actual  amount  of  such  substance  in  the  quantity 
weighed  out  for  analysis. 

IV.  If  percentage  be  required,  multiply  the  last  result  by  100,  and 
divide  by  the  weight  taken  for  analysis. 

(F)  The  quantity  of  the  substance  to  be  weighed  out  for  analysis.  Two 
considerations  are  to  be  kept  in  view,  viz,  :— 

(a)  The   smaller   the   weight   operated   on,  the   greater   will   be   the 

multiplication  of  any  error  in  the  final  result. 

(b)  On  the  other  hand,  the  weighing  out  of  an  amount  of  substance 

that  will  take  more  than  one  buretteful  of  the  standard  solution 
is  to  be  deprecated  as  a  source  of  error. 

The  point  is  to  steer  a  judicious  middle  course,  and  this  can  always  be 
done  by  considering  the  equation,  reducing  it  to  normal  or  decinormal,  etc., 
equivalents,  as  the  case  may  be,  and  then  seeing  how  much  will  be  required 
to  take  a  reasonable  number  of  Cc.  of  the  standard  solution,  supposing  the 
substance  to  be  pure. 

Thus  taking  the  equation  already  considered, 

H,C2O4  .  2H2O  +  2NaHO  =  Na2C2O4 


2)1257  2)79-92 

62-85  3996 

it  is  evident  that  (roughly  speaking)  40  Gm.  of  soda  would  take  1000  Cc.  of 
normal  acid,  and  vice  versa.  If  therefore  we  are  using  a  50  Cc.  burette,  we 
evidently  must  weigh  out  somewhat  less  than 

63-7-20  =  3-15  oxalic  acid 

40-7-20  =  2'OO  sodium  hydrate 

for  titration  by  50  Cc  of  a  normal  solution. 

In  many  cases  the  after-calculation  may  be  altogether  saved  by  weighing 
out  a  previously  determined  quantity,  so  that  the  number  of  Cc.  of  standard 
solution  used  will  at  once  give  the  percentage.  This  idea  is  conveniently 
exemplified  in  the  determination  of  iron  in  salts  thereof.  The  normal  equiva- 
lent of  iron  is  (roughly  speaking)  56,  and  the  solutions  employed  in  its  esti- 
mation are  usually  decinormal,  thus  giving  a  liter  equivalent  of  5*6,  and  a  Cc. 
equivalent  of  '0056.  If  therefore  we  were  to  weigh  out  "56  of  iron,  it  is 
evident  that  each  Cc.  of  a  decinormal  solution  of  a  reagent  for  estimating 
it  would  represent  yj^  of  "56  or  i  per  cent.  Similarly,  if  we  take  "56  of  any 
ferrous  salt  (containing  one  atom  of  iron  in  each  molecule),  each  Cc.  of 
the  volumetric  solution  will  represent  i  per  cent,  of  iron  present.  Supposing 
the  percentage  of  iron  to  be  small  (as  in  Liq.  ferri  perchlor.},  we  would  take 
double  the  quantity  or  1*12  Gm.,  and  then  each  Cc.  would  equal  -5  per  cent. 
of  iron. 

The  rule  may  be  thus  stated  for  all  titration  :  Calculate  the  Cc.  equivalent 
of  the  substance  you  desire  to  estimate,  taking  into  consideration  the  standard 
of  the  solution  you  are  using  (i.e.  normal,  decinormal,  etc.),  and,  having 
multiplied  by  100,  weigh  out  this  quantity  for  analysis.  Then  each  Cc.  of 
your  solution  used  from  the  burette  will  =  i  per  cent,  of  real  substance  in 
the  quantity  weighed  out,  and  fractions  of  a  Cc.  =  similar  fractions  of  i  per 
cent.  When  it  is  not  desired  to  use  a  larger  burette  than  50  Cc.,  only  50 


STANDARD  ACID   SOLUTIONS.  109 

times  the  equivalent  should  be  weighed,  and  then  every  -5  Cc.  =  i  per  cent. 
With  very  accurate  10  Cc.  burettes  graduated  in  -^  Cc.  only  10  times  the 
equivalent  may  be  weighed,  and  then  each  ^  Cc.  =  i  per  cent. ;  but,  as 
before  stated,  the  delicate  work  in  this  respect  leads  frequently  to  error. 

(G)  Precautions  in  direct  titration.  The  standard  solution  may  be  added 
at  first  from  the  burette  to  the  liquid  analyzed  at  the  rate  of  about  '5  Cc. 
at  a  time,  and  the  liquid  should  be  stirred  or  agitated  after  each  addition. 
When  it  is  seen,  by  the  effect  on  the  indicator,  that  the  desired  point  is 
approaching,  the  standard  solution  should  be  added  more  carefully,  and 
finally,  at  the  rate  of  a  single  drop  at  one  time,  till  the  effect  is  obtained. 
The  placing  of  a  white  porcelain  slab,  or  a  sheet  of  white  paper,  under  the 
vessel  containing  the  solution  to  be  analyzed,  helps  us  to  see  the  changes  in 
color  more  accurately.  All  titrations  are  better  done  in  flasks,  the  contents 
of  which  can  be  readily  agitated  by  holding  the  neck,  and  giving  a  circular 
movement  from  the  wrist  between  each  addition  of  the  standard  solution 
from  the  burette. 

(H)  Residual  titration.  This  method  is  employed  when  the  indication 
of  the  completion  of  a  reaction  is  not  easily  seen.  It  consists  in  adding  a 
definite  excess  of  the  reagent,  and  then,  by  means  of  another  volumetric 
solution  which  gives  a  precise  indication,  ascertaining  the  amount  of  the 
reagent  remaining  uncombined.  This  residue,  deducted  from  the  total 
amount  of  original  reagent  added,  will  manifestly  leave  a  difference  due  to 
the  actual  amount  of  that  body  taken  up  in  performing  the  reaction.  Sup- 
posing, for  example,  we  are  analyzing  a  body  (W)  by  finding  how  many  Ccs. 
of  a  volumetric  solution  (S)  would  be  required  to  be  added  until  no  more 
precipitate  forms,  but  that  this  exact  point  is  difficult  to  see.  We  therefore 
choose  another  volumetric  solution  (S2),  that  will  exactly  neutralize  S  in 
presence  of  an  indicator  giving  a  definite  change  of  color  when  the  reaction 
is  complete.  To  W  we  add,  say,  50  Cc.  of  S  (taking  care  that  this  amount 
is  more  than  sufficient  to  entirely  precipitate  W),  and,  having  added  our 
indicator,  we  titrate  with  S2,  of  which  we  will  suppose  we  used  10  Cc,  Then 
508  —  ioS2  —  40  Cc.  S,  required  for  the  original  precipitation. 

And  lastly — 

40  X  the  "Cc.  equivalent"  of  W  —  the  weight  of  real  article  present  in  the  amount 
thereof  weighed  out  for  analysis. 

Having  thus  given  a  general  idea  of  the  mode  of  working,  we  now  com- 
mence to  practise  with  the  chief  standard  solutions  as  follows. 

n,  STANDARD   ACID   SOLUTIONS  (Alkalimetry). 

The  standard  acids  usually  employed  in  volumetric  analysis  are  thus 
prepared  and  used  : — 

(A)  Preparation. 

(I.)  NORMAL    OXALIC  ACID. 
Strength: — H^C^O^.  zH^O  —  125-10  -4-  2  =  62-55  Gm.  per  1000  Cc. 

This  is  made  by  powdering  some  pure  oxalic  acid,  pressing  it  between  the 
folds  of  blotting-paper  (to  remove  any  chance  moisture),  and  weighing  out 
exactly  62-55  Gm.  in  a  tared  beaker.  The  powder  is  then  washed  out  with 
distilled  water  from  the  beaker  into  the  1000  Cc.  measuring  flask,  which  is  nearly 
filled  with  water  and  slightly  warmed  to  aid  solution.  When  all  is  dissolved, 


no  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

more  water  is  poured  in  till  the  solution  arrives  at  the  mark  in  the  neck  of 
the  flnsk,  and  finally  the  whole  is  cooled  down  to  25°  C.,  and  is  once  more 
exactly  made  up  to  the  line  with  water. 

(II.)  TENTH-NORMAL    OXALIC  ACID. 

Strength: — 6*255  Gm. per  1000  Cc. 

Take  100  Cc.  of  the  normal  acid,  wash  into  a  1000  Cc.  flask,  and  make  up  to 
the  mark  with  distilled  water  at  25°  C. 

(III.)  NORMAL  SULPHURIC  ACID. 
Strength: — H^SO^  =  97*35  -4-  2  =  48^675  Gm  per  1000  Cc. 
Mix  30  Cc.  ordinary  strong  sulphuric  acid  (98  per  cent.)  with  900  Cc.  of 
distilled  water,  let  it  cool  to  15°  C.,  and  then  make  up  to  1050  Cc.     This 
rough  acid  is  then  to  be  standardized  as  follows :  — 

(a)  With  normal  alkali.     Put  10  Cc,  of  the  rough  acid  in  a  flask,  add  a 
few  drops  of  phenol-phthalein,  and  run  in  normal  solution  of  KHO  or  NaHO 
until  a  faint   permanent  pink   is  produced.      Note   the  number  of  Cc.   of 
normal  alkali  used,  multiply  by  100,  and  dilute  1000  Cc.  of  rough  acid  to 
this  amount.     Example  loCc.  rough  acid  took  11*2  Cc.  alkali ;  then  1000  Cc. 
acid  are  to  be  diluted  to  1120  Cc.,  and  50  Cc.  of  this  should  exactly  neutralize 
50  Cc.  of  normal  alkali. 

(b)  With  pure  anhydrous  sodium  carbonate  (in    the   absence    of  reliable 
normal  alkali).     Weigh  out  2*6327  Gm.  pure  sodium  carbonate,  and  dissolve 
in  water  in  a  flask ;  add  a  few  drops  of  methyl  orange,  and  run  in  the  rough 
acid  from  a  burette  till  the  yellow  changes  to  pink.     Note  the  number  of  Cc. 
used,  and  then  put  20  times  this  amount  into  the  test  mixer,  and  make  up  to 
1000  Cc.  with  water. 

Note. — Pure  Na2CO3  is  best  made  by  packing  a  percolator  with  good  sodium  bicarbonate, 
and  percolating  with  distilled  water  until  the  fluid,  passing  through,  gives  no  reaction  with 
AgNO.,  or  BaCl2,  after  acidulating  with  HNO3  and  HC1  respectively.  The  contents  of  the 
percolator  are  then  dried  and  heated  to  redness,  and  the  residue  saved  as  "  chemically  pure 
Na.,CO3  for  standardizing  acids." 

(IV.)  HALF-NORMAL   SULPHURIC  ACID. 

Strength: — 24*3375  Gm.  per  1000  Cc. 

Put  500  Cc.  normal  sulphuric  acid  into  a  1000  Cc.  flask,  and  make  it  up  to 
the  mark  with  distilled  water  at  25°  C. 

(V.)  TENTH-NORMAL  SULPHURIC  ACID. 

Strength: — 4*8675  Gm.  per  1000  Cc. 

Put  TOO  Cc.  normal  sulphuric  acid  into  a  1000  Cc.  flask,  and  make  it  up  to 
the  mark  with  distilled  water  at  25°  C. 

(VI.)  NORMAL  HYDROCHLORIC  ACID. 

Strength  :—  HCl  —  36*18  Gm.  per  1000  Cc.  • 

Make  up  130  Cc.  of  ordinary  32  per  cent,  acid  to  1000  Cc.  with  distilled 
water.  This  makes  a  rough  acid  rather  too  strong,  which  is  standardized  as 
follows  : — 

(a)    With  normal  alkali.     Put  10  Cc.  rough  acid  into  a  flask,  and  titrate 


STANDARD  ACID   SOLUTIONS.  m 

with  normal  alkali  as  above  directed  for  sulphuric  acid.  Note  number  of  Cc. 
alkali  used,  multiply  by  100,  and  make  1000  Cc.  of  acid  of  equal  strength. 
Supposing  10  Cc.  rough  acid  took  n  Cc.  normal  alkali,  then — 

IOOO    X    IO 

=  909*1  Cc.  rough  acid  to  be  made  to  1000  Cc. 

50  Cc.  of  this  acid  should  then  exactly  neutralize  50  Cc.  of  normal  alkali. 

(b)  With  crystallized  calcium  carbonate  (in  the  absence  of  reliable  normal 
alkali). 

CaCO3  +  2HC1  =  CaCl2  -f  CO2  +  H2O. 

2)99*35      2)72-36 
49-675        36-18 

Therefore  1000  Cc.  of  normal  acid  should  dissolve  49*675  Gm.  of  CaCOs,  and 
50  Cc.  would  therefore  dissolve  2-4832  Gm. 

Weigh  out  3  Gm.  of  broken  (but  not  powdered)  calc-spar  in  a  small  tared 
beaker,  and  run  on  50  Cc.  of  rough  acid.  When  all  action  has  ceased,  pour  off, 
wash  by  decantation  with  cold  water,  and  then  pour  off  close,  and  dry  the 
beaker  and  contents  by  spontaneous  evaporation  in  a  warm  place.  Weigh 
and  deduct  from  original  weight ;  difference  equals  CaCO3  dissolved.  Sup- 
posing that  this  difference  be  2*75,  then: — 

2731  -  2-483  =  -248; 
therefore  the  acid  was  ^  too  strong,  and  requires  diluting  accordingly. 

(VII.)  HALF-NORMAL  HYDROCHLORIC  ACID. 

Strength: — iS'oQ  Gm. per  1000  Cc. 
Dilute  500  Cc.  normal  acid  to  1000  Cc.  with  distilled  water  at  25°  C. 

(B)  Estimation  of  fixed  Alkaline  Hydroxides  and  Borax. 

Any  of  the  standard  acids  may  be  used  for  this  purpose,  but,  if  normal 
acid  be  employed,  sulphuric  is  preferable,  especially  in  winter,  because  normal 
oxalic  tends  to  crystallize  in  cold  weather.  A  proper  weight  of  the  alkali  having 
been  taken  and  dissolved,  or  if  in  solution  diluted,  a  few  drops  of  solution  of 
methyl-orange  or  litmus  are  added,  and  the  acid  is  run  in  from  the  burette 
until  the  color  changes.  The  addition  of  the  acid  is  made  at  the  rate  of 
about  |  Cc.  at  a  time  (with  constant  agitation  after  each  addition)  until  the 
color  shows  signs  of  turning,  then  the  acid  is  added  in  -^  of  a  Cc.  until 
it  changes. 

In  dealing  with  solid  KHO  or  NaHO,  put  about  i  Gm.  into  a  stoppered 
weighing  bottle  and  weigh  accurately.  Then  dissolve  in  50  Cc.  water  and 
titrate.  For  Aq.  Ammon.  and  Sp.  Ammon.  put  about  3  Cc.  in  a  weighing 
bottle  and  weigh  accurately.  Then  dilute  with  50  Cc.  water  and  titrate, 
using  litmus  indicator. 

The  following  table  shows  the  convenient  quantities  to  weigh,  and  the 
equivalent  weight  of  the  substance  for  each  Cc.  of  normal  acid  used : — 

Name  and  formula.  Gm.  to  weigh.  Equivalent. 

Aqua  ammonise    NH3  3  Cc.  '01693 


fort.  NH3 
Spiritus      ,,         NH3 
Liquor  potassae  KHO 

,,      sodse  NaHO 
Potassium  hydroxide  KHO 
Sodium  NaHO 


3Cc. 

2    Cc. 
27-87 
I9-90 

I  -oo  (about) 

I'OO 


•01693 
•01693 

•05574 
•03976 

•05574 
•03976 


Liquor  calcis  is  titrated  with  ^  acid  and  phenol-phthalein  indicator. 
50  Cc.  is  taken  for  analysis,  and  it  should  use  19  Cc.  acid,  each  Cc.  of  which 
=  -003678  Ca(HO)2. 


112 


VOLUMETRIC  QUANTITATIVE  ANALYSIS. 


The  following  are  typical  equations  of  the  chief  reactions  : — 

(a)  Potassium  hydroxide  or  sodium  hydroxide  or  their  solutions. 

H2SO4  +  2NaHO  =  Na2SO4  +  2H2O. 
HjSO,  +  2KHO  =  K2S04  +  2H20. 

(b)  Liquor  ammonite  fort,  and  liquor  ammonia. 

H2S04  +  2NH, .  H20  =  (NH4)2S04  +  2H2O. 
(f)  Borax  (with  methyl  orange). 

+  NA^Oy .  ioH2O  =  N^SC^  +  H2B4O7  +  ioH,O. 


Equivalent 
of  N  acid. 

•068635 
•08343 


of  £  acid. 

•049705 


(C)  Estimation  of  Alkaline  Carbonates. 

By  titration  with  normal  sulphuric  acid,  with  methyl  orange  as  the  indicator, 
because  the  CO2  given  off  does  not  affect  this  indicator.  The  acid  is  added 
till  the  color  just  changes  from  yellow  to  pink.  The  change  is  better  seen 
when  a  very  small  quantity  of  the  methyl  orange  is  used,  just  sufficient 
to  tinge  the  liquid  pale  yellow.  For  KHCO3  and  Na2CO3  the  U.S.P. 
employs  §  acid. 

The  following  table  shows  the  convenient  quantities  to  weigh,  and  the 
equivalent  of  the  substance  for  each  Cc.  of  normal  acid  or  half-normal 
expended : — 

Gm.  to         Equivalent    Equivalent 
Name  and  formula.  weigh. 

Potassium  bicarbonate  KHCO3       ....  I'OOO 

,,         carbonate  K2CO8 I'ooo 

Sodium  bicarbonate  NaHCO,         ....  2*000 

,,       carbonate  Na2CO3 rooo     .         —        .     -026327 

,,  ,,         monohydrated  Na2CO3 .  H2O    .  rooo     .          —        .     '030797 

The  following  are  typical  equations  for  the  chief  reactions  involved  : — 
{a)  Sodium  carbonate  monohydrated. 

H2SO4  +  Na^CO, .  H2O  =  Na2SO4  +  CO2  +  2H2O. 
(b)  Sodium  bicarbonate. 

H2S04  +  2NaHCOs  =  Na2SO4  +  2CO2  +  2H2O. 

(D)  Estimation  of  Organic  Salts  of  the  Alkalies. 

Organic  salts  of  potassium,  sodium,  or  lithium  are  examined  by  weighing 
out  the  salt  in  a  platinum  or  porcelain  crucible,  and  then  heating  to  redness 
in  contact  with  the  air  until  all  is  perfectly  charred.  The  crucible  is  then 
cooled,  and  its  contents  dissolved  in  boiling  water  and  filtered  into  a  flask, 
and  the  filter  washed  with  boiling  water  until  the  washings  do  not  affect  red 
litmus  paper.  The  contents  of  the  flask  are  then  colored  by  methyl  orange 
and  titrated  with  standard  sulphuric  acid,  in  the  manner  described  above  for 
alkaline  carbonates.  The  ignition  causes  the  conversion  of  the  organic  salt 
into  an  alkaline  carbonate.  The  U.S.P.  employs  £  sulphuric  acid  for  the 
titration  of  organic  salts,  but  it  prefers  to  use  £  HC1  for  Rochelle  salts  and 
sodium  benzoate. 

The  following  table  shows  the  best  quantities  to  weigh  out,  and  the 
equivalent  weight  of  the  substance  for  each  Cc.  of  half-normal  acid  used  : — 

Name  and  formula. 


Potassium  acetate  KC2H,O, 

bitartrate  KHC4H4O8    . 
,,         citrate  K3CaH5O7  . 
,,         sodium  tartrate  KNaC4H4O6 
Sodium  acetate  NaC2H3O2 .  3H2O 
,,         benzoate  NaC7H6O2 
,,         citrate  2Na.,C6H5O7~+  II H2O 
salicylate  NaC7H6O, 


4H20 


Gm.  to 

£acid 

weigh. 

2 
equivalent. 

I  '000 

•04872 

I'OOO 

•09339 

I  -000 

•0507 

rooo 

•070045 

I'OOO 

•06755 

rooo 

•07150 

I'OOO 

•0591 

I'OOO 

•07944  <; 

STANDARD  ACID   SOLUTIONS.  113 

The  following  are  specimens  of  typical  equations  for  some  of  the  above 
reactions,  on  the  model  of  which  the  rest  can  easily  be  constructed  :  — 

(a)  Cream  of  tartar. 

2KHC4H4O6  +  50,  =  K,CO3  +  7CO,  +  sH2O  ; 
then  K,CO3  +  H.,SO4  =  K..SO.  +  CO2  +  H,O  ; 
therefore  H2SO4~=2KHC4H4O6. 

(b)  Neutral  potassium  tartrate. 


2(K2C4H4O(i  .  H2O)  +  sO2  =  2^003  +  6CO2  +  6H.,O  ; 
then  2H2SO4  +  2K2CO3  =  2K2SO4  +  2CO2  +  2H2O~; 
therefore  2lI,SO4  =  2K2C2H4O6  .  H2O. 

(c)  Rochelle  salt. 

2(KNaC4H4Ofi  .  4H.,O)  +  5O2  =  2KNaCO3  +  6CO2+  I2H2O  ; 
then  2KNaCO3  +  2H.,SO4  =  2KNaSO4  +  2CO2  +  2H2O  ; 
therefore  2H2SO4  =  2KNaC4H4O6  .  4H2O  ; 

(d)  Potassium  citrate. 

2K3C6H507  +  902=  3K8CO,  +  9C02  +  sH2O  ; 
then  3K.,CO,  +  3H2SO4  =  3K2SO,  +  3CO2  +  3H2O  ; 
therefore  3H2SO4  =  2K3C6H5O7. 

(E)  Estimation  of  Lead  Salts. 

(a)  Plumbic  acetate. 

Weigh  i  Gm.,  dissolve  in  plenty  of  water  (the  flask  \  full),  with  a  drop  or 
two  of  acetic  acid  to  clarify,  and  then  carefully  drop  in  normal  sulphuric  acid 
till  precipitation  ceases.  The  following  is  the  equation  :  — 

H2SO4  +  Pb(C2H3O2)2  .  3H2O  =  PbSO4  +  2HC2H3O2  +  3H2O. 

(b)  Liquor  plumbi  subacetatis. 

The  U.S.  P.  uses  ^  oxalic  acid  to  precipitate  the  lead  as  oxalate,  and  then 
estimates  the  uncombined  acid  by  potassium  permanganate,  thus  :  — 

If  loGm.  of  the  solution  be  diluted  with  distilled  water,  which  has  been  previously  boiled 
and  cooled,  to  measure  100  Cc.,  and  I3'6  Cc.  of  this  be  added  to  35  Cc.  of  tenth-normal 
oxalic  acid,  contained  in  a  graduated  cylinder,  and,  after  thoroughly  shaking,  the  mixture 
be  diluted  with  distilled  water  to  measure  50  Cc.,  and  again  well  shaken,  then,  after  the 
precipitate  has  settled,  10  Cc.  of  the  clear  solution,  after  diluting  with  about  50  Cc.  of  water 
and  adding  5  Cc.  of  sulphuric  acid,  should  require  not  more  than  2  Cc.  of  tenth-normal 
potassium  permanganate  to  produce  a  permanent  pink  tint  (each  Cc.  of  tenth-normal  oxalic 
acid  required  for  the  precipitation  of  the  I3'6  Cc.  of  the  diluted  solution  corresponding  to 
I  per  cent,  of  lead  subacetate). 

(f)  Cases  where  residual  titration  is  preferable  to  direct  work. 

(a)  Carbonate  of  ammonia. 

The  action  of  indicators  in  the  presence  of  ammonia  not  being,  as  a  rule, 
well  defined,  the  U.S.P.  prefers  to  weigh  out  2  Gm.,  dissolve  in  50  Cc.  each 
of  N  sulphuric  acid  and  water,  boiled  to  expel  CO2,  cool  and  titrate  with 
N.  KHO  litmus  indicator.  The  Cc.  of  KHO  used  deducted  from  50  will 
leave  the  Cc.  of  N  acid  required  to  neutralize  the  2  Gm.  of  ammon.  carb. 
By  the  equation  :  — 

3H2S04  +  2(N3HUC205)  =  3(N  H4)8SO4  -f  4CO2  +  2H2O. 
each  Cc.  of  normal  acid  neutralized  =  '052003  U.S.P.  ammon.  carb. 

(li)  Insoluble  carbonates  and  oxides. 

A  weighed  quantity  is  dissolved  in  a  definite  volume  of  normal  acid  and 
titrated  back  with  normal  alkali.  The  Cc.  N.  KHO  used,  deducted  from  the 

8 


1 14  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

acid  started  with,  gives  the  Cc.  of  acid  required  to  dissolve  the  substance. 
The  U.S.P.  applies  this  to  :— - 

Name.  Gm.  to  weigh.  Acid  to  start  with        Equivalent. 


Lithium  carbonate  '5  .20  Cc. 

Magnesium  carbonate  .  '4  (freshly  ignited)  .         25 

oxide  '4  ,,  -25 

Zinc  oxide  I  'O  .30 


•036755 
'048226 
•02003 
•04039 


In  dealing  with  ZnO  it  is  best  to  use  normal  HC1. 
(c)  Liquor  formaldehydi. 

The  U.S.P.  process  by  oxidizing  the  formaldehyde  to  formic  acid,  and  then 
ascertaining  the  amount  formed  by  residual  titration,  is  as  follows  :— 

Transfer  3  Cc.  of  solution  of  formaldehyde  to  a  well-stoppered  Erlenmeyer  flask,  and 
weigh  accurately.  Add  50  Cc.  of  normal  sodium  hydroxide,  and  follow  this  immediately, 
but  slowly,  through  a  small  funnel,  with  50  Cc.  of  solution  of  hydrogen  dioxide,  to  which 
a  drop  of  litmus  has  been  added,  and  which  has  been  neutralized  with  normal  sodium 
hydroxide.  After  the  reaction  has  ceased  and  the  foaming  has  subsided,  rinse  the  funnel 
and  sides  of  the  vessel  with  distilled  water,  and,  after  allowing  it  to  stand  ten  minutes,  titrate 
back  with  normal  sulphuric  acid,  using  litmus  as  indicator.  Subtract  the  number  of  Cc.  of 
normal  sulphuric  acid  consumed  from  50  (the  number  of  Cc.  of  normal  sodium  hydroxide 
employed),  multiply  the  remainder  by  2-979,  and  divide  the  product  by  the  weight  of  the 
solution  taken  ;  the  quotient  represents  the  percentage,  by  weight,  of  absolute  formaldehyde 
in  the  liquid. 

Ill,  STANDARD  ALKALI  SOLUTION. 

NORMAL   ALKALI. 

Strength  ; — 5574  Gm.  KHO  in  1000  Cc.  or  3976  Gm.  NaHO. 
(A)  Preparation  of  Normal  Potassium  Hydroxide. 

As  the  commercial  alkalies  are  not  pure,  the  U.S.P.  standardized  this 
solution  against  pure  potassium  bitartrate,  which  latter  it  orders  to  be 
obtained  as  follows  : — 

To  100  Gm.  of  potassii  bilartras  U.S.P.  contained  in  a  beaker  is  added  a  mixture  of 
85  Cc.  of  water  and  25  Cc.  of  diluted  hydrochloric  acid  ;  the  covered  beaker  is  then  placed 
upon  a  bath  of  boiling  water  and  the  mixture  digested,  with  occasional  stirring,  for  three 
hours.  After  quickly  cooling,  the  solution  is  drained  off  from  the  precipitate,  which  is 
washed  by  affusion  and  decantation  with  two  successive  portions  of  100  Cc.  each  of  water  j 
after  collecting  the  precipitate  upon  a  plain  filter,  the  washing  with  cold  water  is  continued 
until  the  nitrate,  after  adding  a  few  drops  of  nitric  acid,  ceases  to  become  opalescent  upon 
the  addition  of  silver  nitrate.  The  precipitate  of  potassium  bitartrate  is  then  dissolved  in 
the  smallest  possible  volume  of  boiling  water  (about  1500  Cc. ),  filtered,  and  the  filtrate, 
while  being  rapidly  cooled,  is  constantly  stirred.  When  the  mixture  is  cold,  the  crystalline 
precipitate  is  collected  upon  a  plain  filter,  washed  with  300  Cc.  of  cold  water,  and,  after 
thoroughly  draining,  dried  at  120°  C.  (248°  F.)  until  of  constant  weight.  It  should  be  kept 
in  dry,  securely  stoppered  bottles. 

Having  thus  procured  the  pure  standard,  the  normal  alkali  is  made  as 
follows  : — 

Dissolve  75  Gm.  of  potassium  hydroxide  {potassii  hydroxidum,  U.S.P.], 
in  sufficient  water  to  measure  about  1050  Cc.,  and  fill  a  burette  with  a 
portion  of  this  liquid. 

Into  a  flask  of  the  capacity  of  about  300  Cc.  introduce  9*339  Gm.  of  the 
potassium  bitartrate  and  160  Cc.  of  distilled  water.  Boil  the  liquid  until 
solution  has  taken  place,  add  from  3  to  5  drops  of  phenol-phthalein  indicator, 
followed  by  the  cautious  addition,  from  a  burette,  of  the  potassium  hydroxide 
solution,  frequently  agitating  the  flask,  boiling,  and,  toward  the  end  of  the 
operation,  reducing  the  flow  to  drops  until  the  red  color  produced  by  its 
influx  no  longer  disappears  on  shaking,  but  is  not  deeper  than  pale  pink. 
Note  the  number  of  Cc.  of  the  potassium  hydroxide  solution  consumed,  and 


STANDARD  ALKALI  SOLUTION.  115 

then  dilute  the  remainder  of  the  solution  so  that  exactly  50  Cc.  of  the 
diluted  liquid  at  25°  C.  (77°  F.)  shall  be  required  to  neutralize  the  9*339  Gm. 
of  potassium  bitartrate  used. 

EXAMPLE.  —  Assuming  that  40  Cc.  of  the  stronger  solution  of  potassium  hydroxide  first 
prepared  had  been  consumed  in  the  trial,  then  each  40  Cc.  must  be  diluted  to  50  Cc.,  or  the 
whole  of  the  remaining  solution  in  the  same  proportion  at  25°  C.  (77°  F.).  Thus,  if  IOOO  Cc. 
should  be  still  remaining,  this  must  be  diluted  with  water  to  1250  Cc. 

After  the  liquid  is  thus  diluted,  a  new  trial  should  be  made  in  the  manner 
above  described,  in  which  50  Cc.  of  the  diluted  solution  should  exactly 
neutralize  9*339  Gm.  of  potassium  bitartrate  at  25°  C.  (77°  F.).  If  necessary, 
a  new  adjustment  should  then  be  made  to  render  the  correspondence  perfect. 

Standard  alkali  should  be  kept  in  bottles  fitted  with  a  rubber  cork,  through 
which  passes  a  tube  filled  with  soda-lime  to  prevent  the  entrance  of  CO2  from 
the  air. 

Normal  alkali  diluted  at  25°  C.  from  100  Cc.  to  1000  Cc.  gives  tenth- 
normal,  and  from  20  Cc.  to  1000  Cc.  yields  fiftieth-normal,  alkali,  which 
latter  is  used  in  the  titration  of  alkaloids  (see  Chapter  XL). 

(B)  Preparation  and  Check  of  Half-normal  Alcoholic  Alkali. 

Strength:  —  27*87  Gm.  KHO  in  1000  Cc. 

Dissolve  about  40  Gm.  of  potassium  hydroxide,  which  has  been  broken 
into  small  pieces,  in  about  20  Cc.  of  water,  and  add  sufficient  alcohol  of  '809 
specific  gravity  at  25°  C.  to  measure  1000  Cc.  After  setting  aside  in  a  well- 
stoppered  bottle  for  one  day,  the  clear  supernatant  solution  should  be  quickly 
decanted  into  a  bottle  provided  with  a  well-fitted  rubber  stopper. 

This  rough  solution  is  then  to  be  standardized  against  1-8678  Gm.  of  pure 
potassium  bitartrate  dissolved  in  100  Cc.  water,  exactly  as  above  described,  but 
the  dilution  to  strength  being  of  course  made  with  alcohol  instead  of  water. 

Should  it  be  found  more  convenient,  it  may  also  be  standardized  against 
half-normal  HC1  with  phenol-phthalein  as  indicator.  §  alcoholic  potash  is 
used  in  the  assay  of  certain  organic  substances,  such  as  oils  and  fats  (see 
Chapter  XL). 

(C)  Preparation  and  Check  of  Normal  Sodium  Hydroxide. 

Dissolve  54  Gm.  of  sodium  hydroxide  (Sodii  hydroxidum^  U.S.?.)  in 
sufficient  water  to  measure  1050  Cc.,  and  fill  a  burette  with  a  portion  of  this 
liquid.  Now  proceed  to  standardize  as  above  given  for  normal  KHO. 
50  Cc.  of  normal  NaHO  at  25°  C.  must  exactly  neutralize  9*339  Gm. 
pure  KHC4H4Oc. 

(D)  General  Acidimetry. 

Standard  alkali  is  used  for  taking  the  strength  of  acids  by  simply  weighing 
out  a  quantity  of  the  acid,  and  then  running   in  the  soda  in   presence  of 
phenol-phthalein,  with  the  precaution  already  described  on  page  in.     The 
following  are  some  of  the  more  important  equations  :  — 
O)  KH  O  +  HC1  =  KC1  4-  H,O. 


. 

(0    KHO  +  HC.,HaO,  =  KC,H3O0  +  H..O. 
(V)  2KHO  +  H,S(J4  =  KL,S04  +  2  H2O.  * 
(*)'   2KHO  +  H.C4H4O6=K,C4H4O,  +  2H..O. 
(/)  3KHO  +  H3"C6M5O7  .  H2O  =  K^^O,  +  4H,O. 

The  following  table  shows  the  convenient  amount  of  each  acid  to  weigh  out, 


u6 


VOLUMETRIC  QUANTITATIVE  ANALYSIS. 


the  best  indicator,  and  the  equivalent  weight  of  real  acid  for  each  Cc.  of 
normal  alkali  used  : — 


Quantity  taken.  Indicator.         Equivalent. 

.     5 '96    Gm.     Phenol-phthalein    '05958 
.   23-80 


3-0      Cc. 

J5 

}> 

I'oo    Gm. 

h 

•06154 

1737           5, 

•06950 

3-0      Cc. 

Methyl  orange 

•03618 

3  '62    Gm. 

5  } 

}. 

6-55      5, 

>5 

•06553 

55                    55 

55 

,  , 

4'47       ,5 

Phenol-phthalein 

•08937 

3-0      Cc. 

Methyl  orange 

•06257 

6'257  Gm. 

5» 

,, 

3-0     Cc. 
4-868  Gm. 

55  55 

3723          „ 

I'O 


Phenol-phthalein    '048645 
Methyl  orange         '048675 


Phenol-phthalein    '07446 
•16212 


Name. 

Acidum  aceticum  HCaH3O3    .... 
„  „         dilutum  HC2H3O., 

„         glaciale  HCJLA        - 
,,       boricum  H3BOS          .... 
,,       citricum  H?C6H5O7 .  H,O 
,,       hydrochloricum  HC1 
„  ,,  dilutum  HC1     . 

,,       hypophosphorosum  HPH2O2 

dilutum  HPH2O2. 

lacticum  HC3H5O3    .... 
nitricum  HNO3          .... 

dilutum  HNO3     . 
phosphoricum  H3PO4 

dilutum  H3PO,    . 

sulphuricum  H2SO4  .... 
,,          aromaticum  H.,SO4 

dilutum  H,SO4 
tartaricum  H.,C4H4O6          . 
trichloraceticum  CC13 .  COOH  . 

The  U.S.P.  prefers  to  use  normal  NaHO  for  titrating  boric  and  trichlor- 
acetic  acids,  for  all  the  rest  it  uses  normal  KHO.  Where  Cc.  are  given  in 
the  above  table  instead  of  Gm.,  it  means  that  this  number  of  Cc.  is  to  be  put 
into  a  weighing  bottle  and  then  exactly  weighed  and  calculated  accordingly. 

The  acidimetry  of  phosphoric  acid  is  dependent  on  the  indicator  employed. 
If  we  use  phenol-phthalein  (as  in  U.S. P.),  we  complete  the  formation  of  the 
dibasic  phosphate  at  the  change  of  color  thus  : — 

while  with  methyl  orange  the  completion  of  the  formation  of  the  monobasic 
phosphate  is  indicated  at  the  change  thus  : — 

(6)  H3PO4  +  KHO  =  KH2PO4+H2O. 

Note. — Hydriodic,  hydrobromic,  hydrocyanic,  and  sulphurous  acids  are  not  valued  by  their 
acidity,  but  are  titrated  as  shown  on  pp.  117  and  120. 

IV.   STANDARD   SOLUTION   OF  ARGENTIC   NITRATE. 

Strength: — Tenth-normal  -^  =  i6'869  Gm.  per  1000  Cc. 
'(A)  Preparation. 

Dissolve  16*869  Gm.  of  silver  nitrate  which,  previous  to  weighing,  has 
been  pulverized  and  dried  in  a  covered  porcelain  crucible  in  an  air-bath  at 
130°  C.  (266°  F.)  for  one  hour,  in  sufficient  water  to  measure,  at  25°  C. 
(77°  F.),  exactly  1000  Cc. 

Keep  the  solution  in  dark  amber-colored,  glass-stoppered  vials,  carefully 
protected  from  dust  and  sunlight. 

Check.  As  argentic  nitrate  is  not  always  pure,  this  solution  may  be 
standardized  by  weighing  out  o'ii6  Gm.  of  pure  powdered  sodium  chloride, 
dissolving  it  in  water,  adding  sufficient  potassium  chromate  indicator  to  color 
it  yellow,  and  then  running  in  the  silver  solution,  with  constant  stirring,  until 
the  last  drop  just  causes  the  color  to  change  from  yellow  to  pink.  This 
should  take  20  Cc.  of  silver  solution.  If  the  silver  solution  be  too  strong,  it 
should  be  diluted  by  the  rules  already  given  (see  ante) ;  but  if  too  weak,  it 
must  have  more  AgNO3  added,  and  then  again  checked  and  diluted. 

Preparation  of  pure  sodium  chloride.  Make  a  saturated  solution  of  the  best  commercial 
salt,  and  pass  in  dry  hydrochloric  acid  gas  till  precipitation  ceases.  Separate  the  crystalline 
precipitate,  and  dry  at  a  temperature  below  redness,  but  sufficiently  high  to  expel  all  traces 
of  free  acid. 


STANDARD   SOLUTION  OF  ARGENTIC  NITRATE.         117 

(./>')  Estimation  of  Halogens  in  Soluble  and  Neutral  Salts. 

Tenth-normal  silver  solution  is  used  for  the  estimation  of  haloid  salts  by 
weighing  out  any  quantity  ranging  between  *2  and  '5  (2  or  5  Decigm.), 
dissolving  and  titrating,  K2CrO4  being  used  as  the  indicator,  exactly  as  above 
described.  This  process  is  only  accurate  in  a  perfectly  neutral  solution.  If 
the  solution  be  acid,  then  the  estimation  must  be  done  by  residual  titration 
with  KCNS  (see  p.  119).  The  following  are  some  typical  equations  : — 

(a)  Potassium  bromide 

AgNO3  +  KBr  =  AgBr  +  KNO3. 
(/;)  Ammonium  bromide. 

AgNO3  +  NH4Br  =  AgBr  +  NH,NO3. 
(c)  Potassium  iodide. 

KI  +  AgNO3  =  Agl  +  KNO3. 

Note. — Bromides,  if  adulterated  with  iodides,  will  take  less  silver  than  they  ought,  but  if 
the  impurity  be  chloride,  they  will  take  more.  Therefore  they  must  neither  take  less  nor 
more  than  the  correct  amount. 

The  principle  on  which  an  excess  of  silver  used  can  be  calculated  to  per- 
centage of  KC1  present  in  any  sample  of  KBr  is  best  explained  by  an 
example. 

•236  Gm.  of  impure  KBr  was  found  to  take  21  Cc.  of  -^  AgNOs:  what 
percentage  of  KBr  did  it  contain? 

•236  KBr  would  require  20  Cc.  ~-^  AgNO3. 
•236  KC1      „          „       3r87  Cc.  TNg-  AgN03. 

Theoretical  difference  11-87  due  to  KC1 ; 
but  in  this  case  the  practical  difference  was  3187  — 21  =  io-87. 

Therefore—  10^7x100  =  9r575  per  cent>  of  KBr>  leaving  8-425  KC1, 

1 1  '87 

or  21— 20=1,  and  ^£  =  8-425  per  cent,  of  KC1  and  91  -575  KBr, 

1 1  '87 
which  is  as  nearly  correct  as  can  be  obtained  arithmetically. 

The  following  table  shows  the  salts  thus  estimated,'  with  the  convenient 
quantities  to  weigh  out  and  weight  of  each  salt  equivalent  to  i  Cc.  of 
tenth-normal  silver  nitrate  : — 


Name  and  formula. 
Hydrobromic  acid  (exactly  neutralized)     . 
Ammonium  bromide  NH4C1 
chloride  NH4C1      . 
Lithium  bromide  LiBr      .... 
Potassium  bromide  KBr   .... 
chloride  KC1    . 

Gm.  to  weigh. 
.      '804 
.      -30 
'IO 
.       "20 
.       -30 

Equivalent. 
.      '08036 
'009729 
.       -005311 
'008634 
.       '011822 
'OO74O4. 

,,         iodide  KI          ... 

•t;o 

'016476 

Sodium  bromide  NaBr      .... 
,,       chloride  NaCl 

.     -30 

'IO 

.      -010224 
'005806 

,,        iodide  Nal  . 

•ro 

'014878 

Strontium  bromide  SrBr.,  +  6H.,O 
Zinc  bromide  ZnBr.2           .... 
,,    chloride  ZnCl./  . 

.       -30 

•     '30 
•     '3° 

.      -017647 
.      -OIIl8l 
'006763 

(C)  Estimation  of  Hydrocyanic  Acid. 

Silver  solution  is  also  used  for  taking  the  strength  of  hydrocyanic  acid, 
which  may  be  done  by  two  methods  as  follows  : — 

(A)  Half  precipitation  process.  By  this  method  the  ~$  AgNOa  is  added  in 
presence  of  excess  of  alkali  with  a  little  potassium  iodide  as  indicator.  The 
silver  at  first  combines  with  the  alkali  and  then  forms  a  soluble  double 
cyanide  of  silver  and  the  alkali,  and  so  soon  as  this  reaction  is  complete  a 
precipitate  is  produced  with  the  indicator.  Thus  when  this  precipitate 
appears  it  shows  that  exactly  half  the  cyanide  present  is  combined  with  the 


n8  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

silver,  therefore  each  Cc.  of  -^  silver  solution  used  =  '-{(~  or  '005368  HCN. 
The  U.S. P.  instructions  are  as  follows  :— 

If  5  Gm.  of  diluted  hydrocyanic  acid  be  diluted  with  distilled  water  to  measure 
50  Cc.,  then  26-9  Cc.  (26-84  Cc.)  of  this  solution,  after  the  addition  of  5  Cc. 
of  ammonia  water  and  3  drops  of  solution  of  potassium  iodide  (20  per  cent, 
strength),  should  require  for  the  production  of  a  slight  permanent  precipitate 
the  addition  of  not  less  than  10  Cc.  of  tenth-normal  silver  nitrate. 

If  the  dilution,  etc.,  be  calculated,  it  will  be  seen  that  2  684  Gm.  of  U.S. P. 
acid  are  taken.     This  requires  10  Cc.  yjj-  AgNOj,  therefore  : — 
•005368  x  10 --05368  and  '05368  x  loo  =  2  ^  cem    ^  RCN 

2  '604 

Potassium  cvanide  is  done  in  the  same  way,  using  '647  Gm.,  and  as 
AgNO3  =  2KCN,  each  Cc.  of  T\  AgNO3  =  "012940  KCN. 

(B)  Complete  precipitation  process.  Put  the  hydrocyanic  acid  into  a  100  Cc. 
flask  with  sufficient  water  and  MgO  to  make  an  opaque  mixture  of  about 
10  Cc.  Add  2  or  3  drops  of  solution  of  potassium  chromate,  and  titrate  as 
directed  for  haloid  salts.  The  equation  being 

HCN  +  AgNOs  =  AgCN  +  HNO:i, 
each  Cc.  of  silver  used  will  represent  '002684  HCN. 

The  U.S. P.  employs  this  method  for  the  assay  of  oil  of  bitter  almond  as 
follows : — 

Mix,  in  a  100  Cc.  flask,  i  Gm.  of  the  oil  of  bitter  almond  to  be  tested,  with 
sufficient  water  and  freshly  precipitated  magnesium  hydroxide  (free  from  chlor- 
ides) to  make  an  opaque  mixture  of  about  50  Cc.  Add  to  this  2  or  3  drops  of 
potassium  chromate,  and  then  from  a  burette  add  tenth-normal  silver  nitrate 
until  a  red  tint  is  produced  which  does  not  again  disappear  by  shaking ;  not 
less  than  7-5  Cc.  nor  more  than  14*9  Cc.  of  tenth-normal  silver  nitrate  should 
be  required,  each  Cc.  corresponding  to  0*002684  Gm.  of  hydrocyanic  acid. 

V.  STANDARD  SOLUTION  OF  SODIUM  CHLORIDE. 

Strength: — Tenth-normal  ~  =  5*837   (5*84)   Gm.  per  1000   Cc. 

(A)  Preparation. 

Dissolve  5*837  Gm.  pure  NaCl  in  900  Cc.  of  water,  and  when  brought 
exactly  to  15°  C.  make  up  1000  Cc.  Each  Cc.  =  '005837  Gm.  real  NaCl. 
Pure  sodium  chloride  is  made  as  above  described  (p.  r  16),  or  perfectly  colorless 
and  transparent  crystals  of  rock  salt  may  be  employed. 

(B)  Uses. 

For  the  estimation  of  silver  in  solutions  of  its  salts,  the  titration  being 
continued  (with  good  stirring  occasionally)  until  the  last  drop  causes  no 
further  precipitate  of  AgCl.  Insoluble  salts,  such  as  Ag2O,  are  dissolved 
in  a  sufficiency  of  dilute  nitric  acid,  avoiding  any  great  excess.  Tenth-normal 
NaCl  can  also  be  employed  to  check  the  strength  of  tenth-normal  AgNOs 
solution  (which  it  should  exactly  equal  Cc.  to  Cc.),  as  more  convenient  than 
weighing  out  NaCl  every  time.  The  following  table  gives  the  equivalent 
for  each  Cc.  of  tenth-normal  NaCl : — 

Name  and  formula.  Gm.  to  weigh.  Equivalent. 

Argentic  nitrate  AgNO.t         ...        '5  ...      '016869 

,,         oxide  Ag./J     ....        '232  .          .          .      '011506 

Argenti  nitras  tlilufus    .          .          .  I  'oo  .          .          .      '016869 

When  the  silver  solution  is  neutral,  it  is  often  better  to  add  a  known 
volume  of  tenth-normal  NaCl,  more  than  sufficient  to  precipitate  all  the  silver, 
and  then  having  added  potassium  chromate  as  indicator,  to  proceed  by 
residual  titration  with  tenth-normal  AgNOs.  The  U.S. P.  applies  this  method 
to  all  forms  of  silver  nitrate. 


STA  NDA  RD  SOL  UT1ON  OF  POT  A  SSIUM  THIO  C  YA  NA  TE.     \  \  g 

VI.  STANDARD  SOLUTION  OF  POTASSIUM  THIOCYANATE 
(SULPHOCYANIDE). 

Strength: — Tenth-normal  -^  =  9*653  Gm.  per  1000  Cc. 

(A)  Preparation  and  Check. 

Dissolve  10  Gm.  of  potassium  thiocyanate  (sulphocyanide)  in  1000  Cc.  of 
water.  This  solution  is  a  little  too  strong,  and  must  then  be  standardized  as 
follows: — Take  in  a  flask  10  Cc.  of  tenth-normal  silver  nitrate,  acidulate  with 
3  Cc.  of  nitric  acid,  and  then  add  as  indicator  3  Cc.  of  a  solution  of  ferric 
ammonium  sulphate  (10  per  cent,  strength).  Now  titrate  with  the  crude 
thiocyanate  solution  by  shaking  constantly  until  a  slight  permanent  reddish 
tint  is  produced.  The  thiocyanate  will  first  precipitate  the  silver  as  thio- 
cyanate, and  when  that  is  finished  will  strike  the  well-known  reddish  color 
of  ferric  thiocyanate  with  the  indicator.  The  red  is  always  produced  when 
the  solution  is  dropped  in,  but  it  disappears  on  shaking  so  long  as  any  silver 
remains  unprecipitated.  Note  the  number  of  Cc.  of  crude  thiocyanate  used, 
and  make  every  10  Cc.  of  that  solution  up  to  this  number.  Thus  supposing 
that  10  Cc.  tenth-normal  silver  nitrate  took  10*5  Cc.  crude  sulphocyanate,  and 
we  had  980  Cc.  left  to  make  correct,  then— 

io-5*  980  =  I029cc. 
10 

So  that  980  Cc.  made  up  with  distilled  water  to  1029  Cc.  will  give  true 
tenth-normal  thiocyanate,  of  which  50  Cc.  should  exactly  balance  50  Cc. 
tenth-normal  silver  nitrate  when  tried  again  in  a  similar  manner.  Each  Cc. 
of  the  perfected  solution  will  then  contain  "09653  KCNS. 

(£)  Estimation  of  Silver  in  Acid  Solutions. 

This  is  done  exactly  as  above  described,  and  may  be  usefully  applied  to 
any  compound  of  silver  soluble  in  nitric  acid.  The  equivalents  for  each 
Cc.  are  '010712  Ag  and  '016869  AgNOs- 

(C)  Estimation  of  Haloid  Salts  in  Acid  Solutions. 

This  is  an  application  of  residual  titration,  known  as  Volhard's  method, 
and  is,  in  certain  cases,  a  much  better  idea  for  the  estimation  of  haloid 
salts  than  the  direct  method  with  the  chromate  indicator,  because  it  may 
be  used  in  the  presence  of  nitric  acid,  thus  enabling  a  chloride,  bromide, 
or  iodide  to  be  estimated  in  presence  of  a  phosphate  or  other  salt  which 
precipitates  silver  in  a  neutral  solution.  It  depends  upon  entirely  pre- 
cipitating the  chloride  in  the  presence  of  nitric  acid  by  a  known  volume 
of  tenth-normal  silver  nitrate,  and  then  estimating  the  excess  thereof,  left 
uncombined  with  the  chloride,  by  standard  solution  of  ammonium  thiocyanate 
(sulphocyanate),  using  solution  of  ferric  ammonium  sulphate  for  the  indicator 
as  above  described.  The  U.S.P.  applies  it  to  the  estimation  of  the  iodide 
in  syr.  acidi  hydriodiri  and  in  syr.  ferri  iodidi.  It  takes  3173  Gm.  of  syr.  ac. 
hydriodici,  makes  it  up  to  50  Cc.  with  water,  and  then  uses  10  Cc.  of  this 
solution  for  analysis  with  10  Cc.  water,  8  Cc.  f^  AgNO3,  5  Cc.  diluted  nitric 
acid,  and  3  Cc.  ferric  ammonium  sulphate  solution,  and  then  titrates  with 
y^  KCN  as  above.  For  syr.  ferri  iodidi  it  makes  up  10  Cc.  to  100  Cc.  with 
water,  and  takes  15-4  Cc.  for  analysis,  using  15  Cc.  water,  6  Cc.  of  TN^  AgNOs, 
2  Cc.  each  diluted  nitric  acid  and  ferric  ammonium  sulphate,  and  finally 
titrating  with  -^  KCN  as  already  described,  and  not  more  than  3  Cc.  or  r  Cc. 
respectively  of  KCN  should  be  required.  Taking  the  case  of  syr.  ferri  iodidi, 
we  have — 

Tenth-normal  silver  added      .          .     6  Cc. 
,,  sulphocyanate  taken      I  Cc. 

Difference        .         .     5  Cc.,  due  to  the  silver  precipitated  as  iodide. 


120  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

Then   5  x  '015365  =  '076825   real    FeI2   present,    or   5    per   cent,  of  the 
i '54  Gm.  syrup  really  started  with. 

The  process  is  also  employed  by  the  U.S. P.  in  the  analysis  of  the 
following : — 

Name  and  formula.  Gra.  to  weigh.  Equivalent. 

Hydiiodic  acid  (dil.)  HI.          .         .         .     2-54  .         .      '012690 

Strontium  iodide  SrI2       ....        '50  .         .      '022301 

Zinc  iodide  ZnL,       .....        -50  ..      '015835 

VII.  STANDARD  SOLUTION  OF  IODINE. 

Strength: — Tenth-normal^—  12  '59  Gm.  per  1000  Cc. 
(A)  Preparation  and  Check. 

Weigh  out  1 2 '59  Gm.  of  pure  iodine,  and  place  it  in  a  1000  Cc.  flask  with 
1 8  Gm.  of  potassium  iodide  and  about  200  Cc.  of  water,  agitate  till  dissolved, 
make  up  to  1000  Cc.  with  water,  and  preserve  in  small  stoppered  bottles  in  a 
dark  place.  Each  Cc.  =  '01259  I. 

Preparation  of  pure  iodine.  Heat  powdered  iodine  in  a  flat  porcelain  dish 
on  a  boiling-water  bath,  with  constant  stirring,  for  20  minutes.  Rub  it  up 
in  a  glass  mortar  with  5  per  cent,  of  its  weight  of  pure  potassium  iodide,  and 
return  to  the  dish.  Place  a  clean,  dry  funnel  over  the  dish  and  heat  on  a 
sand  bath,  when  the  pure  iodine  will  sublime  and  collect  on  the  funnel,  from 
which  it  is  detached,  and  kept  in  a  well-stoppered  bottle. 

Check.  To  standardize  the  strength  of  the  solution  (if  desired),  test  it 
against  '2  Gm.  (2  Decigm.)  of  pure  As2Os  as  hereafter  described. 

(B)  Estimation  of  Arsenious  Acid. 

For  arsenious  acid,  weigh   out  i   Decigm.  of  the  As2C>3,  and   dissolve  it 
in  boiling  water  by  the  aid  of  ten  times  its  weight  of  NaHCO3.     Let  it  cool, 
add  some  mucilage  of  starch,  and  titrate  with  the  iodine  solution  until  a  faint 
permanent  blue  color  is  obtained.     Then  apply  the  equation  :— 
2l,  4-  As,O3  +  5H,O - 2H3AsO,  +  4HI. 

Each  Cc.  of  y^  iodine  used  =  '004911  A?2Os. 

For  liquor  acidi  arseniosi  or  liquor  potassii  arsenitis  use  24*6  Gm.  in  100  Cc. 
water,  adding  2  Gm.  NaHCOs,  and  then  titrating. 

(C)  Estimation  of  Sulphurous  Acid  and  Sulphites. 

For  sulphurous  acid  weigh  out  2  Gm.  from  a  stoppered  bottle,  and  dilute 
it  with  25  Cc.  of  water.  Add  starch  mucilage,  and  run  in  the  iodine  solution 
until  the  faintest  possible  per?nanent  blue  appears.  Then  apply  the  equation : — 

I2  +  H,O  +  SO, .  H,O  =  H,SO4  +  2HI ; 
whereby  each  Cc.  TNg-  iodine  used  =  '003180  SO2. 

For  sulphites  dissolve  in  25  Cc.  of  water  and  proceed  as  above. 

The  following  table  shows  the  convenient  amounts  to  weigh,  and  the 
equivalent  for  i  Cc.  yjj-  iodine  of  the  salts  named  : — 

Name  and  Formula.  Gm.  to  weigh.  Equivalent. 

Potassium  sulphite  K,SOj .  2H,O          .        .        .  -485  .  .     -009648 

Sodium  bisulphite  NaHSO3           ....  '25  .  -005168 

,,         sulphite  NaJ5O3. 7 H2O    ....  '63  .  -012520 

Sulphur  dioxide  (in  sulphurous  acid)  SO2      .          .  2-oo  .  .     '003180 

(D)  Estimation  of  Antimony  Potassium  Tartrate. 

This  salt  absorbs  iodine  on  a  s'milar  principle  of  indirect  oxidation  to  that 
already  shown  for  As2C>3.     The  reaction  may  be  thus  expressed : — 
KSbOC4H406 .  H,0  +  I,  +  4NaHC03  +  H2O  =  KNaC ,H,O6  +  2NaI  +  NaSbO3  +  4CO2  +  4H2O. 
Therefore  each  atom  of  iodine  can  oxidize  |  of  the  molecular  weight  of  the 


STANDARD  SOLUTION  OF  SODIUM  THIOSULPHATE.      121 

tartrate.  In  practice  i  Gm.  of  the  salt  is  dissolved  in  sufficient  water  to 
measure  100  Cc.,  and  of  this  33  Cc.  is  taken  for  analysis.  20  Cc.  of  cold 
saturated  solution  of  sodium  bicarbonate  is  added,  together  with  a  little 
starch  mucilage,  and  the  whole  is  titrated  with  -^  iodine  till  a  faint  per- 
manent blue  is  produced.  The  number  of  Cc.  of  iodine  used  multiplied  by 
•016495  gives  the  amount  of  real  tartrate  present,  which  should  be  100  per  cent. 
The  NaHCOs  is  added  to  convert  the  insoluble  potassium  bitartrate  shown 
in  the  equation  into  soluble  KNaC^jOe,  and  to  combine  with  the  free 
antimonic  and  hydriodic  acids  also  produced. 

VIII.  STANDARD  SOLUTION  OF  SODIUM  THIOSULPHATE  ("HYPO"), 

Strength:  -^  =  24-646  Gm.  Na^O^.^H^O  per  1000  Cc. 
(A)  Preparation  and  Check. 

Dissolve  30  Gm.  of  crystallized  sodium  thiosulphate  (hyposulphite)  in 
sufficient  water  to  make  1100  Cc.  at  15°  C.  Put  10  Cc.  of  this  "crude  hypo" 
into  a  flask,  add  a  little  starch  mucilage,  and  titrate  with  tenth-normal  iodine 
until  a  faint  permanent  blue  is  obtained.  Note  the  number  of  Cc.  of  iodine 
used,  and  make  every  10  Cc.  of  the  "crude  hypo"  up  to  this  bulk  with 
distilled  water.  Suppose,  for  example,  10  Cc.  of  "crude  hypo"  took  10*8  Cc, 
^  iodine,  and  we  had  1080  Cc.  of  the  crude  solution  left,  then — 

1080  XI0'8  =  1166-4  Cc.  of  correct  ^  "hypo." 

50  Cc.  of  the  finished  solution  must  be  again  titrated,  and  must  take  50  Cc, 
of  YJJ- iodine.  It  must  be  kept  in  dark  amber-colored  bottles  and  carefully 
protected  from  dust.  Each  Cc.  will  contain  '024646  real  Na3SsO3.  5H2O. 

Tenth-normal  "hypo"  deteriorates  rapidly,  even  under  the  most  favorable 
circumstances,  and  must  therefore  be  checked  against  -^  iodine  each  day  it 
is  used,  and  any  deficiency  found  allowed  for  in  the  calculations.  Thus, 
suppose  we  checked  our  "  hypo  "  as  above  explained,  and  found  that  20  Cc. 
of  it  only  took  19  Cc.  of  iodine,  and  then  we  used  the  same  "hypo"  in  an 
analysis  which  absorbed  40  Cc.,  we  would  correct  thus  : — 

19x40^^  Cc  rea]  _N_  «hypo,>  actually  absorbed  ; 

and  then  38  x  Cc.  equivalent  of  substance  analyzed  gives  the  amount 
thereof  present. 

Practical  analysts,  knowing  that  they  must  always  check  in  any  case, 
always  titrate  with  the  "crude  hypo,"  and  do  not  trouble  to  make  it  exactly 
Tk,  preferring  simply  to  make  a  calculated  correction  on  every  analysis,  as 
indicated  by  the  check  for  the  day  previously  done  against  £$  iodine. 

Solution  of  sodium  thiosulphate  is  used  as  follows  : — 

(B)  Estimation  of  Free  Iodine. 

Put  about  5  Gm.  in  a  weighing  bottle,  weigh  accurately,  and  dissolve  in 
50  Cc.  water  by  the  aid  of  i  Gm.  potassium  iodide,  and  then  run  in  "hypo" 
till  the  color  is  reduced  to  that  of  a  pale  sherry ;  lastly,  add  starch  mucilage, 
and  go  on  till  the  blue  produced  by  the  starch  is  just  bleached.  Then  by 
the  equation, 

2(Na2S2O3  -  5H,O)  +  I,  =  2NaI  4-  Na,S4Os  +  ioH2O, 
it  is  evident  that  each  Cc.  ~  "hypo  "  =  '01259  iodine. 

(C)  Estimation  of  Free  Chlorine  or  Bromine. 

For  chlorine  water. 

Weigh  17-7  Gm.  from  a  stoppered  bottle,  pouring  it  directly  into  a  flask 


122  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

containing  2  Gm.  of  potassium  iodide  previously  dissolved  in  50  Cc.  of  water, 
and  then  titrate  with  "hypo"  as  already  described  under  (B). 

The  Cl  first  liberates  an  equivalent  quantity  of  iodine  from  the  KI,  and 
the  "  hypo  "  then  acts  upon  the  I2  so  set  free,  thus  :— 


, 

2'Na,S,,O3  .  5H..O)  +  I,  =  2NaI  +  Na,S4Oe  +  ioH,,O. 
Therefore  each  Cc.  TN^  "hypo"  =  '003518  chlorine. 

On  the  same  principle  we  would  titrate  bromine  wafer,  but  in  that  case 
each  Cc.  TN^  "hypo"  would  =  '007936  bromine. 

(D)  Estimation  of  Available  Chlorine. 

For  chlorinated  lime. 

Introduce  into  a  stoppered  weighing-bottle  between  3  and  4  Gm.  of 
chlorinated  lime  and  weigh  accurately  ;  triturate  this  thoroughly  with  50  Cc. 
of  water,  transfer  the  mixture  to  a  graduated  vessel,  together  with  the  rinsings, 
and  add  sufficient  water  to  make  1000  Cc.  After  thoroughly  shaking,  add  to 
TOO  Cc.  of  the  mixture  i  Gm.  of  potassium  iodide  and  5  Cc.  of  diluted 
hydrochloric  acid.  Lastly,  titrate  with  "  hypo,"  adding  starch  mucilage 
towards  the  end  of  the  titration  as  already  described  under  (,#).  Then  by 
the  equations— 

O)  CaOCl.,  +  2HC1  =  CaCl,  +  H.,O  +  Cl,, 

(<*)  CU  +  2ia  =  2KC1  +  L, 

(0  2(Na,S,O3  .  5H2O)  +  1,  =  2NaI  +  Na,S4O(i  +  ioH2O, 

we  come  to  the  result  already  shown  for  chlorine  water  —  namely,  that 

2(Na,S2O3.  5H,O)  =  I,  =  C1,. 

Therefore  each  Cc.  —^  "hypo"  =  '003518  Gm.   "available  chlorine"  in  all 
chlorinated  compounds. 
Liquor  sodce  chlorinates. 

Use  7  Gm.,  with  50  Cc.  water,  2  Gm.  KI.,  and  10  Cc.  hydrochloric  acid, 
and  proceed  as  for  chlorinated  lime.  The  action  and  calculations  are  the 
same,  only  differing  in  the  first  equation,  which  is  :  — 

Na2OCl,  +  2HC1  =  2NaCl  +  H2O  +  C12. 

(E)  Estimation  of  Iron  in  Ferric  Salts. 

When  excess  of  potassium  iodide  is  added  to  a  ferric  salt  in  solution  in  the 
presence  of  hydrochloric  acid,  and  the  whole  is  digested  at  40°  C.  in  a  closely 
stoppered  bottle  for  half  an  hour,  the  iron  in  the  ferric  salt  is  reduced  to  the 
ferrous  state,  and  an  equivalent  quantity  of  iodine  is  liberated.  Thus,  taking 
ferric  chloride,  we  would  have  :— 

Fe,ClG  +  2KI  =  2FeCl,  +  2KC1  +  I,. 

Therefore  each  atom  of  iron  so  reduced  liberates  i  atom  of  iodine,  and  then 
the  iodine  so  liberated  is  titrated  with  -^  "hypo";  and  thus  we  see  — 

Na,S./)3.  5H,O  =  I,=  Fe2. 
And  so  each  Cc.  of  -^  "hypo"  =  '00555  iron  in  the  ferric  salt  under  analysis. 

In  practice  we  usually  weigh  '555  Gm.  of  a  solid  ferric  salt,  or  i'n  Gm.  of 
a  ferric  liquor,  put  it  into  a  stoppered  bottle  of  about  100  Cc.  capacity, 
dissolve  in  or  dilute  with  15  Cc.  of  water,  add  2  Cc.  of  hydrochloric  acid  and 
i  Gm.  of  potassium  iodide,  and  quickly  close  the  bottle.  The  whole  is  then 
placed  in  a  basin  of  water  heated  to  40°  C.  (104°  F.),  and  maintained  at  that 
temperature  for  half  an  hour.  At  the  expiration  of  that  time  the  bottle  and 
contents  are  cooled  to  15°  C.,  and  starch  mucilage  having  been  added,  the 
contents  are  titrated  in  the  bottle  with  -^  "  hypo."  The  number  of  Cc.  of 
"  hypo  "  used  (after  correction  for  check  if  fiecessary)  are  then  multiplied  by 
the  Cc.  equivalent  of  iron  as  above  given.  The  point  of  the  process  is  to  get 


STANDARD   SOLUTION  OF  BROMINE.  123 

no  loss  of  iodine  vapour  during  the  heating,  and  yet  to  take  care  that  the 
bottle  does  not  hurst  by  the  expansion  of  the  contained  air  by  the  heat. 
When  -555  Gm.  of  a  ferric  salt  is  taken,  each  Cc.  of  T^  "hypo"  used  =  i  per 
cent,  of  iron  ;  but  when  n  i  Gm.  of  a  liquor  is  started  with,  then  each  Cc.  =  '5 
per  cent,  of  iron. 

(F)  U.S. P.  Assay  of  Reduced  Iron  (Ferrum  redactuni). 

Introduce  about  2*6  Gm.  of  iodine  into  a  100  Cc.  flask  and  weigh 
accurately,  then  add  6  Cc.  of  water,  2  Gm.  of  potassium  iodide,  and  0*555 
Gm.  of  reduced  iron.  Securely  stopper  the  flask,  and,  after  thoroughly  mixing 
the  contents  by  rotating  the  flask,  set  it  aside  for  one  hour.  Then  dilute  the 
contents  with  sufficient  distilled  water  to  make  the  liquid  measure  exactly 
100  Cc.,  mix  well,  and  to  25  Cc.  of  this  solution  slowly  add  tenth-normal 
sodium  thiosulphate  with  constant  stirring,  until  the  last  trace  of  brown  color 
has  been  discharged.  Divide  the  weight  of  iodine  taken,  by  0*02518,  and 
subtract  from  the  quotient  twice  the  number  of  Cc.  of  tenth-normal  sodium 
thiosulphate  used  ;  the  remainder  represents  the  percentage  of  metallic  iron 
present  in  the  reduced  iron,  and  this  should  not  be  less  than  90  per  cent. 

Note. — The  percentage  purity  of  the  iodine  employed  should  be  accurately  determined  by 
a  previous  experiment,  and  in  place  of  the  2'6  Gm.  above  directed,  its  equivalent  in  pure 
(100  per  cent.)  iodine  may  be  taken  (see  p.  120). 

IX.  STANDARD  SOLUTION  OF   BROMINE. 

Strength:  —  =  7*936  Gm.  per  1000  Cc. 
(A)   Preparation  and  Check. 

As  it  is  impossible  to  keep  an  actual  solution  of  bromine,  we  make  and 
keep  a  mixed  one  of  a  bromide  and  bromate  in  such  proportion  that  when 
acidulated  with  a  fixed  quantity  of  acid  (5  Cc.  HC1)  shall  give  a  definite 
amount  of  free  bromine  by  the  equation — 

5KBr  +  KBrOj  +  6HC1  =  6KC1  +  3Br,  +  3H,O. 
To  do  this  we  follow  the  procedure  of  the  U.S. P.  as  follows  : — 

Dissolve  3  Gm.  of  sodium  bromate  and  50  Gm.  of  sodium  bromide  (or 
3*2  Gm.  of  potassium  bromate  and  50  Gm.  of  potassium  bromide)  in  enough 
water  to  make,  at  or  near  15°  C.,  900  Cc.  Of  this  solution  transfer  20  Cc., 
by  means  of  a  pipette,  into  a  bottle  having  a  capacity  of  about  250  Cc., 
provided  with  a  glass  stopper ;  add  75  Cc.  of  water,  next  5  Cc.  of  pure  hydro- 
chloric acid,  and  immediately  insert  the  stopper.  Shake  the  bottle  a  few 
times,  then  remove  the  stopper  just  sufficiently  to  quickly  introduce  5  Cc. 
20  per  cent,  solution  of  potassium  iodide,  taking  care  that  no  bromine  vapour 
escapes,  and  immediately  stopper  the  bottle.  Agitate  the  bottle  thoroughly, 
remove  the  stopper  and  rinse  it  and  the  neck  of  the  bottle  with  a  little  water 
so  that  the  washings  flow  into  the  bottle,  and  then  add  from  a  burette 
j^-  sodium  hyposulphite  until  the  iodine  tint  is  exactly  discharged,  using 
towards  the  end  a  few  drops  of  starch  indicator.  Note  the  number  of  Cc. 
of  the  sodium  hyposulphite  thus  consumed,  and  then  dilute  the  bromine 
solution  so  that  equal  volumes  of  it  and  of  T^  sodium  hyposulphite  will  exactly 
correspond  to  each  other  under  the  conditions  mentioned  above. 

EXAMPLE. — Assuming  that  the  20  Cc.  of  the  bromine  solution  have  required  25*2  Cc.  of 
the  hyposulphite  to  completely  discharge  the  iodine  tint,  the  bromine  solution  must  be 
diluted  in  the  proportion  of  20  to  25*2.  Thus,  if  850  Cc.  of  it  are  remaining,  they  must  be 
diluted  with  water  to  measure  1071  Cc. 

After  the  solution  is  thus  diluted,  a  new  trial  should  be  made  in  the 
manner  above  described,  in  which  25  Cc.  of  the  ~  sodium  hyposulphite 


I24  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

should  exactly  discharge  the  tint  of  the  iodine  liberated  by  the  bromine  set 
free  from  the  25  Cc.  of  bromine  solution. 

Keep  the  solution  in  dark  amber-colored  glass-stoppered  bottles. 

(£}  Estimation  of  Phenol  (Carbolic  Acid). 

The  bromine  solution  is  added  in  fixed  excess,  more  than  sufficient  to 
convert  all  the  phenol  into  insoluble  tribromophenol— C6H2Br3 .  OH — and 
the  bromine  remaining  undecomposed  is  titrated  with  KI,  starch,  and  -*•$ 
"  hypo  "  as  above  described.  The  number  of  Cc.  of  "  hypo  "  used  having 
been  deducted  from  the  Cc.  of  -^  bromine  started  with,  the  difference 
x  "001556  =  real  phenol  present  in  the  amount  of  sample  weighed  out  for 
analysis.  The  following  example  is  taken  from  the  U.S. P. : — 

Assay  of  Phenol.  Dissolve  1*556  Gm.  of  the  phenol  to  be  valued  in  a 
sufficient  quantity  of  water  to  make  TOGO  Cc.  Transfer  25  Cc.  of  this  solu- 
tion (containing  0*0389  Gm.  of  phenol)  to  a  glass-stoppered  bottle  having  a 
capacity  of  about  200  Cc.,  add  30  Cc.  of  tenth-normal  bromine,  than  5  Cc.  of 
hydrochloric  acid,  and  immediately  insert  the  stopper.  Shake  the  bottle 
repeatedly  during  half  an  hour,  then  remove  the  stopper  just  sufficiently  to 
introduce  quickly  5  Cc.  of  an  aqueous  solution  of  potassium  iodide  (i  in  5), 
being  careful  that  no  bromine  vapour  escapes,  and  immediately  stopper  the 
bottle.  Shake  the  latter  thoroughly,  remove  the  stopper  and  rinse  it  and  the 
neck  of  the  bottle  with  a  little  water,  so  that  the  washings  may  flow  into  the 
bottle,  and  then  add  i  Cc.  of  chloroform  and  shake  well.  Add,  from  a 
burette,  tenth-normal  sodium  thiosulphate  until  the  iodine  tint  is  exactly 
discharged,  and  does  not  reappear  after  thorough  agitation.  Note  the  number 
of  Cc.  of  tenth-normal  sodium  thiosulphate  consumed  (which  should  not 
exceed  6  Cc.).  The  percentage  of  absolute  phenol  is  found  by  subtracting 
the  number  of  Cc.  of  tenth-normal  sodium  thiosulphate  used,  from  30  (the 
number  of  Cc.  of  bromine  originally  added),  and  multiplying  the  remainder 
by  4. 

X.    ANALYSIS    BY   DIRECT    OXIDATION. 

(A)  General  Principles. 

The  two  chief  direct  oxidizers  employed  in  analysis  are  potassium  per- 
manganate and  potassium  bichromate,  both  of  which  part  with  oxygen  in 
presence  of  sulphuric  acid,  but  in  different  proportions.  These  actions  are 
represented  by  the  following  equations  : — 

With  bichromate.     K,Cr,O7  +  4H,SO4  =  K, SO4  +  Cr,(SO4)3  +  4H,O  +  O3 ; 
therefore  each  molecular  weight  of  bichromate  gives  three  atomic  weights  of 
oxygen. 

With  permanganate.     K,Mn,O8  +  3H,SO4  =  K.SO4  +  2MnSO4  +  O5  +  3H2O  ; 
therefore  each   molecular  weight  of  permanganate  gives  five  atomic  weights 
of  oxygen. 

We  have  already  seen  that  the  theoretical  N  solution  of  hydrogen  is  i  Gm. 
per  1000  Cc.,  or  'coi  in  each  Cc.  ;  and  looking  to  the  formula  of  the  simplest 
compound  of  H  and  O,  namely  water,  we  notice  that  i  atom  O  combines 
with  2  atoms  H.  It  therefore  follows  that  i  Gm.  of  H  would  combine  with 
15-88  (T 6)  H-  2  =  7-98  (8)  Gm.  of  O.  A  theoretical  N  solution  of  O  would 
thus  be  7-94  Gm.  per  1000  Cc.,  and  a  ~$  solution  would  be  794  Gm.  O  per 
1000  Cc.,  and  would  contain  '000794  oxygen  in  each  Cc.  In  oxidation 
analysis,  therefore,  a  -^  solution  of  any  oxidant  is  that  weight  in  Gm.  per  1000 
Cc.  which  will  give  off  "794  Gm.  oxygen  under  the  conditions  in  which  it  is 
used. 


ANAL  YSIS  B Y  DIRECT  OXIDA T1ON.  1 2 5 

Thus  taking  bichromate  we  have 

K2C r2O7  =  292 -28  -r  6  =  4*8713  Gm.  per  1000  as  a  yjj-  oxidant ; 
and  ion  permanganate  we  have 

K2Mn2O8  =  3i3'96 -7-10  =  3-1396  Gm.  per  1000  as  a  y^  oxidant. 

Each  Cc.  of  either  of  these  solutions  will  give  '000794  available  oxygen,  and 
will  therefore  produce  exactly  the  same  effect  in  the  analysis  of  anything 
readily  oxidized. 

Oxidants  are  never  employed  in  stronger  solution  than  y^,  and  frequently 
for  delicate  work  they  are  made  centinormal  (T5nr)- 

There  are  almost  unlimited  cases  in  which  such  solutions  may  be  applied 
to  the  various  bodies  capable  of  undergoing  a  definite  change  by  oxidation, 
but  the  most  common  applications  are  : — 

(i)  For  the  estimation  of  ferrous  salts.  If  we  look  at  the  simplest  equation 
for  the  transference  of  iron  from  the  ferrous  to  the  ferric  state,  we  find 

2FeO  +  O  =  Fe2O3. 

So  we  observe  that  i  atomic  weight  of  O  can  oxidize  2  atomic  weights  of  Fe, 
or  that 

27-94  =  Fe  55-5; 

molecular  weight 
tnerefore  each  Cc.  of  A-  oxidant  =  '00555  metallic  iron  or  — 

10,000 

of  any  ferrous  salt  containing  i  atom  of  iron  in  its  molecule.  Either  of  the 
oxidants  may  be  employed  for  the  estimation  of  ferrous  salts. 

Take,  for  example,  crystallized  ferrous  sulphate.     We  have  the  equations  : — 

With  bichromate. 
K,Cr2O7  +  6FeSO4 .  7H,O  +  7H,SO4  =  3Fe,(SO4)3  +  K,,SO4  +  Cr2(SO4)3  +  49H2O. 

With  permanganate. 

K2Mn2O8  4-  ioFeSO4 .  7H2O  +  8H2SO4  =  5Fe,(SO4)3  +  K2SO4  +  2MnSO4  +  78H2O. 
In  certain  ferrous  salts,  such  as  phosphate  or  arseniate^  the  molecules  of 
which  contain  Fes,  it  is  evident  that  from  the  equation 
K,Cr2O7  +  2Fe3(AsO4),  +  7H,SO4  =  Fe,(SO4)3  +  2Fe2(AsO4)2  +  K2SO4  +  Cr2(SO4)3  +  7H2O. 

,    ~       c  N       . ,  .  molecular  weight  x  3 

each  Cc.  ot  YTT  oxidant  would  equal of  such  salt. 

10,000 

Such  salts  are  included  in  the  B.P.,  but  not  in  the  U.S.P. 
The  following  table  gives  the  equivalents  of  i  Cc.  of  either  oxidant  for 
some  of  the  more  important  ferrous  salts  :— 

Name  and  formula.  Gm.  to  weigh  Equivalent. 


Iron  (in  ferrous  salts)  Fe 
Ferrous  carbonate  (in  ferri  carb.  sacch.)FeCO3. 
sulphate  (cryst.)  FeSO4 .  7H2O     . 


anhydrous  FeSO 
(dried  U.S.P.)  2  FeSO4 
phosphate  B.  P.  Fe3(PO4)., .  8H..O 
arseniateB.P.  Fe3(AsO4)2   . 


76 
•895 
•836 
744 


•00555 

"011505 

'027601 

•015085 

•017767 

•016733 

•014867 


(2)  For  the  estimation  of  oxalic  acid  and  oxalates.     The  following  equation 
shows  that  to  oxidize  oxalic  acid  or  an  oxalate  requires  i  atomic  weight  of 
oxygen  for  each  molecule  of  oxalate  : — 

H2C,O4 .  2H2O  +  O  =  2CO2  +  3H2O  ; 

therefore  each   Cc,  of  a  ^  oxidant  will  equal  H2C2O4  •  2H2O  Qr  .Qo6 

20,000 

equivalent  to  each  Cc.      The  only  oxidant  employed  in  this  case  is  per- 
manganate. 

(3)  For  the  estimation  of  hydrogen  dioxides  and  peroxides.     By  the  equations 

H,O,+ 


i26  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

it  is  evident  that  i  atomic  weight  of  O  acts  with   i  molecular  weight  of  the 

molecular  weight      r,,, 
peroxide  ;  therefore  i  Cc.  £*  oxidant  =  -  —     1  he  only  oxidant 

20,000 

available  is  permanganate,  and  the  process  is  official  in  the  U.S.  P.  :  — 

Name  and  formula.  Equivalent. 

Hydrogen  dioxide  (in  solution)H,O,          .....     -001688 
Barium  dioxide  BaO2         ........      '008408 

(4)  For  the  estimation  of  hypophosphorous  add  and  hypophosphites.     The 
equation 


shows  that  each  molecular  weight  of  hypophosphorous  acid  requires  2  atomic 

t,       r  •  i  molecular  weight      ,„,. 

weights  of  oxygen  ;  therefore  each  Cc.  TC7  oxidant  =  -  —       1  he 

40,000 

only  oxidant  used  in  this  case  is  permanganate,  and  the  table  gives  the  usual 
information,  but  the  U.S.  P.  does  not  employ  this  method  :  — 

Name  and  formula.  Gm.  to  weigh.  Equivalent. 


Hypophosphorous  acid  HPH2O2 . 
Sodium  hypophosphite  NaPH2O2 
Potassium  ,,  KPH2O2 

Calcium  ,,  Ca(PH.,O.,)2 

Ferric  Fe,(PH2O2)6 


•001639 
•0021837 
•002588 
•0021108 


•002309 
(5)  For  equivalent  liberation  of  halogens  from  haloid  salts.     The  equation 

2KI  -i-  O  +  H2O  =  2KHO  + 12 

shows  that  each   atomic  weight   of  nascent  oxygen   can   liberate  2  atomic 
weights  of  a  halogen  from  its  salts;  therefore  each  Cc.  of  ~  oxidant  can 

atomic  weight    r  t,      ,    i  i_  r-       c  \ 

liberate  -  -  of  the  halogen.      1  nus  each  Cc.  of  y^  permanganate  is 

10,000 

equivalent  to  '003518  Cl,  '007936  Br,  or  '01259  I. 

The  liberated  halogen  is   then  estimated  by  means  of  ^  sodium  thio- 
sulphate  ("hypo")  as  already  described. 

(B]  Preparation  and  Uses  of  Solution  of  Potassium  Permanganate. 

Strength:  f^  =  3*1396  Gm.  K^Mn^O^,  in  icoo  Cc. 
(1)  Preparation  and  Check. 

(a)  Solution  for  immediate  use.     Dissolve  3*5  Gm.   K2Mn2O8  in  1000  Cc. 
of  recently  boiled  and  cooled  distilled  water.     This  is  the  crude  solution,  and 
must  now  be  checked  by  placing  10  Cc.  •£$  oxalic  acid  in  a  small  flask,  adding 
i  Cc.  of  pure  strong  sulphuric  acid,  and  titrating  this  liquid  while  hot  with  the 
crude  solution  (over  a  sheet  of  white  paper)  till  a  faint  permanent  pink  is 
obtained.    Note  the  number  of  Cc.  of  solution  used,  and  dilute  the  remainder 
of  the  crude  solution  with  similarly  treated  water  until  50  Cc.  exactly  corre- 
spond to  50  Cc.  TN^  oxalic  acid. 

Thus,  if  10  Cc.  -£$  oxalic  took  9-2  Cc.  crude  permanganate,  we  would  have 
920  Cc.  up  to  1000  Cc.,  and  then  we  would  (after  confirmation  of  50  Cc. 
against  50  Cc.  acid)  have  true  y\  permanganate.  This  solution  cannot  be 
depended  on  unless  just  made,  and  if  a  solution  is  to  be  made  and  stocked 
more  precautions  must  be  taken.  These  precautions  are  so  well  explained  in 
U.S. P.  that  the  directions  therein  given  cannot  be  improved,  and  they  are  as 
follows : — 

(b)  Preparation  of  f^  permanganate  for  stock.     Introduce  about  3*3  Gm. 
of  pure,  crystallized  potassium  permanganate  \potassii  permanganas,  U.S.P.] 
into  a  flask,  add  1000  Cc.  of  distilled  water,  and  boil  for  about  five  minutes. 
Close  the  flask  with  a  plug  of  absorbent  cotton,  and  set  aside  for  at  least  two 


ANALYSIS  BY  DIRECT  OXIDATION.  127 

days,  so  that  suspended  matter  may  deposit.     After  the  lapse  of  this  time, 
pour  off  the  clear  portion  of  the  solution  into  a  glass-stoppered  bottle. 

The  water  to  be  employed  for  diluting  this  solution  (which  is  still  too 
concentrated)  should  be  prepared  as  directed  under  Distilled  Water  \aqua 
destillata,  U.S. P.],  adding,  however,  about  i  Gm.  of  potassium  permanganate 
to  the  water  in  the  retort  before  beginning  the  distillation. 

1.  Introduce  into  a  flask  10  Cc.  of  an  accurately  standardized  tenth-normal 
oxalic  acid  V.S.,  add  i  Cc.  of  pure,  concentrated  sulphuric  acid,  and  before 
this  mixture  cools,  gradually  add,  from  a  burette  provided  with  a  glass  stop- 
cock,   small   quantities    of  the   permanganate    solution  to  be   standardized, 
shaking  the  flask  after  each  addition  and  reducing  the  flow  to  drops  toward 
the  end  of  the  operation.     When  the  last  drop  of  the  permanganate  solution 
added  is  no  longer  decolorized  but  imparts  a  pinkish  tint  to  the  liquid,  which 
remains  permanent  for  one-half  minute,  note  the  number  of  Cc.  consumed, 
and  then  dilute  the  trial  permanganate  solution  with  the  specially  prepared 
distilled  water  so  that  it  will  correspond,  volume  for  volume,  at  25°  C.  (77°  F.), 
with  the  tenth-normal  oxalic  acid  V.S.  (note  example  under  2). 

2.  Tenth-normal  potassium  permanganate  V.S.  may  also  be  standardized 
as  follows : 

To  a  solution  of  about  i  Gm.  of  potassium  iodide  \J>otassii  iodidum^  U.S.?.], 
in  10  Cc.  of  diluted  sulphuric  acid,  contained  in  a  flask,  add,  from  a  burette 
provided  with  a  glass  stop-cock,  20  Cc.  of  the  potassium  permanganate 
solution  to  be  standardized ;  then  dilute  the  mixture  at  once  with  about 
200  Cc.  of  distilled  water.  An  accurately  standardized  tenth-normal  sodium 
thiosulphate  V.S.  is  then  slowly  added  from  a  burette,  while  the  mixture  is 
vigorously  shaken,  until  the  color  is  discharged.  Note  the  number  of  Cc.  of 
the  latter  consumed,  then  dilute  the  permanganate  solution  so  that  equal 
volumes  of  the  two  solutions  correspond  to  each  other  under  the  same 
conditions  at  25°  C.  (77°  F.). 

EXAMPLE. — Assuming  that  25  Cc.  of  the  tenth-normal  sodium  thiosulphate  V.S.  were 
required  to  decolorize  the  liberated  iodine  of  the  mixture,  then  each  20  Cc.  of  the  potassium 
permanganate  solution  must  be  diluted  with  the  specially  prepared  distilled  water  to  25  Cc., 
or  the  whole  of  the  remaining  solution  in  the  same  proportion.  Thus,  if  920  Cc.  remain,  it 
should  be  diluted  to  measure  1150  Cc.  at  25°  C.  (77°  F.). 

After  the  potassium  permanganate  solution  is  thus  diluted,  a  new  trial 
should  be  made  in  the  manner  above  described,  in  which  20  Cc.  of  this 
solution  should  require  exactly  20  Cc.  of  the  tenth-normal  sodium  thio- 
sulphate V.S.  to  decolorize  the  mixture.  If  necessary,  a  new  adjustment 
should  be  made  to  render  the  correspondence  perfect. 

Potassium  permanganate  V.S.  should  be  kept  in  well-closed  glass-stoppered 
bottles,  and  only  burettes  provided  with  glass  stop-cocks  should  be  employed 
in  titrating  with  it.  Even  when  properly  prepared  and  preserved,  this  solution 
should  be  restandardized  frequently. 

(c)  Standardization  of  Crude  permanganate  solution  by  a  ferrous  salt.  Many 
persons  prefer  this  method  to  that  already  given  above  with  oxalic  acid.  The 
salt  employed  is  ferrous  ammonium  sulphate,  FeSO4.  (NH4)2SO4.  6H2O, 
which  contains  practically  \  of  its  weight  of  metallic  iron.  The  process  is 
performed  by  weighing  out  7  Gm.  of  ammonia-ferrous  sulphate  (  =  *i  Gm. 
real  Fe),  dissolving  it  in  100  Cc.  of  distilled  water,  acidulating  with  6  Cc.  of 
dilute  sulphuric  acid  (i  to  5),  and  then  titrating  with  the  permanganate  until 
a  slight  permanent  pink  is  produced,  not  disappearing  on  shaking.  To  see 
the  color,  a  sheet  of  white  paper  should  be  placed  under  the  flask  containing 
the  iron  solution,  and,  at  the  conclusion  of  the  process,  the  number  of  Cc. 
having  been  noted,  the  solution  is  diluted,  on  the  usual  principles,  until  it 
takes  exactly  18  Cc.  to  oxidize  -i  Gm.  Fe. 


128  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

(2)  Estimation  of  Ferrous  Salts. 

\Yeigh  out  a  proper  amount  of  the  ferrous  salt,  dissolve  in  25—50  Cc.  water, 
acidulate  with  6  Cc.  diluted  sulphuric  acid  (i  to  5),  place  the  flask  over  a 
sheet  of  white  paper,  and  titrate  with  y^  permanganate  till  a  faint  permanent 
pink  is  produced.  Note  the  number  of  Cc.  used,  and  multiply  by  the  Cc. 
equivalent  of  the  salt  under  analysis  (see  table,  p.  125). 

(3)  Estimation  of  Oxalic  Acid  and  Oxalates. 

This  is  performed  as  already  described  under  "preparation  and  check"  of 
permanganate  solution  (see  p.  126).  The  great  point  is  that  the  solution 
to  be  analyzed  should  be  sufficiently  warm  to  give  off  visible  steam.  The 
equivalent  of  oxalic  acid  has  been  already  given  (see  p.  125). 

(4)  Estimation  of  Hydrogen  Dioxide  (Peroxide). 

The  principle  of  this  estimation  has  been  already  explained  and  the  equiva- 
lents given  on  p.  126.  The  following  would  be  the  practical  procedure : — 

Assay  of  sohttion  of  hydrogen  dioxide.  Dilute  10  Cc.  of  the  solution  with 
•water  to  make  100  Cc.  Transfer  16*9  Cc.  of  this  liquid  (containing  1*69  Cc. 
of  the  solution)  to  a  beaker,  add  5  Cc.  of  diluted  sulphuric  acid,  and  then 
from  a  burette  -^  potassium  permanganate,  until  the  liquid  just  retains  a  faint 
pink  tint  after  being  stirred.  Each  Cc.  of  the  yrr  potassium  permanganate 
corresponds  to  *i  of  absolute  hydrogen  dioxide  or  0*329  volumes  of  oxygen. 

(5)  Estimation  of  Nitrites. 

This  is  best  done  by  adding  excess  of  -^  permanganate,  and  then  perform- 
ing a  residual  titration  with  oxalic  acid.  The  following  is  an  example  of  this 
method  as  applied  by  the  U.S. P.  to  the  assay  of  sodium  nitrite : — 

If  to  30  Cc.  of  tenth-normal  potassium  permanganate,  diluted  with  about 
150  Cc.  of  distilled  water,  5  Cc.  of  sulphuric  acid  and  10  Cc.  of  a  solution  of 
i  Gm.  of  sodium  nitrite  in  sufficient  distilled  water  to  make  100  Cc.  be 
successively  added,  the  liquid  brought  to  a  temperature  of  40°  C.  (104°  F.) 
and  allowed  to  stand  for  five  minutes,  not  more  than  375  Cc.  of  tenth-normal 
oxalic  acid  should  be  required  to  decolorize  the  solution  (each  Cc.  of  tenth- 
normal  potassium  permanganate  consumed  corresponding  to  0*0034285  Gm. 
of  pure  sodium  nitrite). 

(C)  Preparation  and  Uses  of  Solution  of  Potassium  Bichromate. 

Strength  :  ^  =  4-8713    Gm.  K^Cr^Oi  in  1000  Cc. 
(1)  Preparation. 

Dissolve  4*8713  Gm.  pure  potassium  bichromate  in  enough  distilled  water 
to  make  exactly  1000  Cc.  at  15°  C.  (59°  F.). 

Note. — Pure  K2Cr2O7,  in  addition  to  ordinary  tests,  should  (according  to  the  U.S. P.) 
conform  to  the  following  tests  : — In  a  solution  of  '5  Gm.  of  the  salt  in  10  Cc.  of  water 
rendered  acid  by  "5  Cc.  of  nitric  acid,  no  visible  change  should  be  produced  either  by 
barium  chloride  (absence  of  sulphate)  or  by  silver  nitrate  (absence  of  chloride*).  In  a  mixture 
of  10  Cc.  of  the  aqueous  solution  (i  in  20)  with  i  Cc.  of  ammonia  water,  no  precipitate 
should  be  produced  by  ammonium  oxalate  (absence  of  calcium}. 

(2)  Uses. 

(a)  For  the  estimation  of  ferrous  salts.  An  appropriate  quantity  of  the 
ferrous  salt  is  weighed  and  dissolved  in  a  flask  in  50  Cc.  of  warm  distilled 
water  if  soluble,  or,  if  insoluble,  dilute  H2SO4  is  added  till  the  salt  dissolves. 
While  this  is  proceeding  a  white  porcelain  slab  is  dotted  over  with  drops 
(from  a  glass  rod)  of  potassium  ferricyanide  indicator  (see  p.  106) ;  the 
contents  of  the  flask  are  then  acidified  with  10  Cc.  of  dilute  H2SO4  (i  to  5), 
and  titrated  with  the  ^  bichromate  till  a  drop  taken  from  the  flask  on  the 
end  of  a  glass  rod  and  touched  on  one  of  the  spots  of  the  indicator  on 
the  slab  just  ceases  to  give  any  blue,  thus  showing  that  all  the  iron  has 


FEHLING'S  STANDARD  SOLUTION  OF  COPPER.          129 

been  oxidized  from  the  ferrous  to  the  ferric  state.  The  number  of  Cc.  ^ 
bichromate  used  x  the  Cc.  equivalent  of  the  salt  under  analysis  (see  table, 
p.  124)  gives  the  weight  thereof  present  in  the  amount  taken  for  analysis. 
The  process  should  be  conducted  rapidly  to  avoid  spontaneous  oxidation  as 
far  as  possible.  When  applied  to  metallic  iron  or  ferrum  redactum,  the  metal 
should  be  dissolved  in  diluted  HgSO*  in  a  flask  fitted  with  a  cork,  through 
which  passes  a  narrow  tube  to  admit  the  outward  passage  of  the  hydrogen 
evolved  and  to  prevent  ingress  of  air.  With  ferrous  phosphate  and  sac- 
charated  ferrous  carbonate,  it  is  better  to  replace  sulphuric  acid  by 
hydrochloric  acid  and  phosphoric  acid  respectively. 

(b}  for  alkalimetry.  Solution  of  bichromate  is  sometimes  employed  to 
set  the  strength  of  volumetric  solutions  of  alkalies.  In  this  case  the  strength 
is  not  based  upon  the  oxygen  evolved  with  acid,  but  upon  the  following 
equation : — 

K2Cr207  +  2KHO  =  2K2CrO4  +  H,O. 

Therefore  \  molecular  weight  K2Cr2O7  =  i  molecular  weight  of  KHO,  i.e. 
K,CrX>7 .  29378  (294)  -f-  2  =  146-89  (147)  =  55-99  (56)  KHO. 

For  alkalimetry,  therefore,  a  decinormal  bichromate  solution  would  be  made 
by  dissolving  14*689  K2Cr2O7  in  water  at  15°  C.  to  1000  Cc.,  and  each  Cc.  of 
such  solution  would  neutralize  '0056  KHO  or  '004  NaHO.  If,  therefore,  we 
set  50  Cc.  of  this  alkalimetric  -~j  bichromate  against  50  Cc.  of  alkali,  the 
latter  will  be  correct  -—,  and  any  acid  in  turn  set  against  that  would  also  be 
~.  The  indicator  used  is  phenol-phthalein,  as  in  ordinary  alkalimetry.  This 
is  a  very  useful  method  of  standardizing  volumetric  alkali  when  we  are  not 
absolutely  certain  of  the  purity  of  our  oxalic  acid.  The  alkali,  however, 
cannot  be  made  stronger  than  y^,  because  147  Gm.  of  K2Cr2O7  would  not 
dissolve  in  1000  Cc.  of  water,  and  therefore  it  is  no  use  for  normal  alkalies. 

(<;)  For  equivalent  liberation  of  halogens.  The  y^-  bichromate  (as  oxidant) 
can  do  the  same  work  in  this  respect  as  the  -£$  permanganate,  and  on  the 
same  principles.  The  process  is  done  in  presence  of  sulphuric  acid,  and 
the  liberated  iodine  is  titrated  with  •£$  "  hypo." 


XI,  FEHLING  S   STANDARD   SOLUTION   OF   COPPER. 

(A)  Manufacture  and  Check  by  the  Ordinary  Method. 

This  solution  is  used  for  the  estimation  of  sugars,  and  is  made  in  two  parts, 
as  follows  : — 

No.   I. 

Take  of 

Sulphate  of  copper  .         ....     346*4  grains  or  34*64  Gm. 
Distilled  water ^  a  sufficiency. 

Dissolve  the  sulphate  of  copper  in  a  portion  of  the  water,  and  dilute  the 
solution  with  more  of  the  water  to  the  volume  of  5000  grain-measures,  or 
500  Cc. 

No.  2. 
Take  of 

Caustic  soda     ......     if  ounce  or  76^5  Gm. 

Tartarated  soda 4    ounces  or  1 75  'O  Gm. 

Distilled  water a  sufficiency. 

Dissolve  the  caustic  soda  and  tartarated  soda  in  a  portion  of  the  water, 
and  dilute  the  solution  with  more  of  the  water  to  5000  grain-measures,  or 
500  Cc. 

When  required  for  use,  mix  equal  volumes  of  the  solutions  No.  i  and 
a  9 


1 30  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

No.   2.     On  heating  the  liquid  in  a  test-tube  to  boiling,   it  should  remain 
perfectly  clear.     Each  10  Cc.  of  this  liquid  will  represent — 

Glucose -oso    Gm. 

Maltose "0807    „ 

Lactose '0678    „ 

Inveited  cane  sugar 'O475    »> 

Inverted  starch '045      „ 

To  check  Fehling's  solution,  weigh  out  "475  Gm.  of  pure  sugar-candy  and 
dissolve  it  in  100  Cc.  of  water  in  a  small  flask ;  add  3  drops  of  strong  HC1, 
and  boil  briskly  for  ten  minutes  to  invert  the  cane  sugar  into  glucose.  Let 
it  cool,  neutralize  with  KHO,  and  then  make  up  exactly  to  100  Cc.  with 
distilled  water.  Place  this  liquid  in  a  burette  arranged  over  a  basin  placed 
over  the  gas,  and  containing  10  Cc.  of  Fehling's  solution  and  50  Cc.  of 
water.  When  the  contents  of  the  basin  are  boiling,  run  in  the  sugar  solution 
until  all  blue  color  is  destroyed.  Then  note  the  number  of  Cc.  of  sugar 
solution  used,  and  whatever  that  number  may  be,  it  will  contain  the  equivalent 
in  sugar  of  10  Cc.  of  "  Fehling."  If  the  "Fehling"  be  correct,  10  Cc.  of  the 
standard  sugar  will  be  used  to  entirely  precipitate  it. 

It  is  usually  necessary  to  do  the  estimation  twice,  first  roughly  and  then 
accurately,  using  the  second  time  drops  of  K^FeCeNg  acidulated  with  acetic 
acid  on  a  slab,  as  an  indicator  for  the  disappearance  of  the  last  trace  of  Cu 
from  solution. 

Another  way  of  inverting  a  solution  of  cane  sugar  into  glucose  is  to  add  one- 
tenth  of  its  bulk  of*  fuming  HC1,  heat  gradually  up  to  68°  C.,  and  then  cool. 
This  is  the  better  method  when  the  solution  is  to  be  used  for  the  polariscopic 
estimation  of  sugar  (see  Chapter  XII.). 

(£}  Manufacture  and  Check  by  Pavy's  Method. 

Cuprous  oxide  dissolves  in  ammonia,  forming  a  colorless  liquid.  Taking 
advantage  of  this  point,  Pavy  treats  an  ammoniacal  cupric  solution  at  a 
boiling  temperature  with  sufficient  saccharine  solution  to  exactly  discharge 
the  blue  color.  The  advantage  of  this  method  over  that  above  described 
lies  simply  in  the  fact  that  there  is  no  bulky  red  precipitate  to  interfere  with 
the  ready  observation  of  the  end  reaction.  To  prepare  the  test  solution, 
dissolve  20*4  Gm.  of  Rochelle  salt  and  the  same  weight  of  caustic  potash 
in  distilled  water;  dissolve  separately  4*158  Gm.  of  pure  cupric  sulphate  in 
more  water  with  heat ;  add  the  copper  solution  to  that  first  prepared,  and 
when  cold  add  300  Cc.  of  strong  ammonia,  and  distilled  water  to  i  liter. 
The  process  is  conducted  as  follows  :  TO  Cc.  of  the  ammoniated  cupric  solution 
(=  0-005  Gm.  of  glucose)  are  diluted  with  20  Cc.  of  distilled  water,  and 
placed  in  a  small  flask.  This  is  attached  by  means  of  a  cork  to  the  nozzle  of 
a  burette,  fitted  with  a  glass  stopcock,  and  previously  filled  with  the  saccharine 
solution  previously  diluted  to  a  fixed  bulk.  The  cork  of  the  flask  should  be 
traversed  by  a  small  bent  tube,  to  permit  steam  to  escape.  Now  heat  the 
flask  until  the  blue  liquid  boils.  Turn  the  stopcock  in  order  to  allow  the 
saccharine  solution  to  flow  into  the  hot  solution — which  should  be  kept  at  the 
boiling-point — at  the  rate  of  about  100  drops  per  minute  (not  more  nor  much 
less),  until  the  azure  tint  is  exactly  discharged.  Then  stop  the  flow,  and 
note  the  number  of  Cc.  used.  That  amount  of  saccharine  solution  will 
contain  5  milligrams  of  glucose.  To  render  the  determination  as  accurate 
as  possible,  the  solution  for  analysis  should  be  diluted  to  such  an  extent 
that  not  less  than  4  nor  more  than  7  Cc.  are  required  to  decolorize  the 
solution. 

To  find    the  total  amount  of  sugar,  multiply  0-005   DV  tne  original  total 


ESTIMA  TION  OF  PHOSPHORIC  A  CID.  13 1 

bulk  (in  Cc.)  of  the  sugar  solution  started  with,  and  divide  the  product  by 
the  number  of  Cc.  of  solution  used  from  the  burette.  To  observe  easily 
the  exact  end  reaction,  a  piece  of  paper  or  other  white  body  should  be  placed 
behind  the  flask.  Mr.  Stokes  uses  the  half  of  an  ordinary  opal  gas  globe 
fixed  in  the  proper  position.  If  the  operator  objects  to  the  escape  of  the 
waste  ammoniacal  fumes,  they  may  be  conducted  by  a  suitable  arrangement 
into  water  or  dilute  acid.  For  a  special  apparatus  for  this  purpose  see  the 
Analyst,  vol.  xii. 

(C]  Estimation  of  Sugar. 

The  sugar  weighed  must  not  exceed  '5  Gm.,  and  must  be  dissolved  in 
100  Cc.  of  water.  If  the  sugar  be  either  glucose  or  maltose  or  lactose,  it  is 
titrated  directly  ;  but  if  cane  sugar,  it  is  first  inverted  as  above  described. 
By  always  placing  10  Cc.  of  "  Fehling  "  in  the  basin,  then  whatever  number 
of  Cc.  of  sugar  solution  we  use,  that  number  will  contain  the  equivalent  of 
10  Cc.,  and  we  have  only  to  calculate  : — 

As  No.  of  Cc.  used  :  Total  volume  of  sugar  solution  :  Equivalent  of  10  Cc.  *'  Fehling  "  of 
the  sugar  in  question  :  Real  sugar  present  in  the  quantity  weighed  out  for  analysis. 

(D)  Estimation  of  Starch. 

Starch  is  weighed  and  boiled  in  a  flask  with  water  containing  dilute  hydro- 
chloric acid,  under  an  upright  condenser,  for  some  hours.  It  is  then  cooled, 
neutralized  with  potassium  hydrate,  diluted  to  a  fixed  volume  (not  stronger 
than  i  in  200),  and  then  the  solution  so  made  is  titrated  into  10  Cc*  of 
"  Fehling."  A  much  improved  process  will  be  found  in  Chapter  X. 


XII.  ESTIMATION  OF   PHOSPHORIC  ACID 

is  performed  by  means  of  a  standard  solution  of  uranic  nitrate  in  the  presence 
of  sodium  acetate.     The  necessary  solutions  are  : — 

1.  Standard  solution  of  uranic  nitrate,  made  by  dissolving  70  Gm.  in 
900  Cc.  of  water,  and  then,  after  ascertaining  its  strength  by  performing  an 
analysis  of  50  Cc.  of  the  standard  phosphate  solution,  diluting  with  water  so 
that  50  Cc.  will  correspond  exactly  to  50  Cc.  of  that  solution.     If  absolutely 
pure  uranic  nitrate  were  obtainable,  theory  requires  the  solution  of  71  Gm. 
in  i  liter  of  water  to  yield  a  solution  which  will  balance  the  standard  phos- 
phate (each  i  Cc.  =  '01  Gm.  of  P2Os). 

2.  Standard  phosphate  solution,  made  by  dissolving  50*42  Gm.  of  perfectly 
pure   disodium   hydrogen   phosphate  in  i  liter  of  water,  when  each  i  Cc. 
will  equal  *oi  Gm.  of  PgOs. 

3.  A  solution  of  100  Gm.  of  sodium  acetate  and  100  Gm.  of  acetic  acid  in 
water,  and  the  whole  diluted  to  i  liter. 

4.  Finely  powdered  potassium  ferrocyanide. 

To  perform  the  process,  the  solution  of  the  phosphate  in  about  50  Cc.  of 
water  is  placed  in  a  basin  on  the  water  bath,  mixed  with  5  Cc.  of  solution 
No.  3  (sodic  acetate),  and  No.  i  (uranic  nitrate)  is  run  in  from  a  burette, 
until  a  drop  taken  from  the  basin  on  to  a  white  plate  just  gives  a  brown  color, 
when  a  little  powdered  ferrocyanide  is  cautiously  dropped  into  its  center.  The 
number  of  Cc.  of  uranic  solution  used  having  been  noted,  the  usual  calculations 
are  to  be  applied. 

After  repeated  trials  upon  50  Cc.  of  the  standard  phosphate  solution,  so 
as  to  thoroughly  adjust  the  strength  of  the  uranic  solution,  and  at  the  same 


i32  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

time  accustom  the  eye  to  observe  the  exact  moment  of  the  appearance  of  the 
brown  coloration,  the  process  may  be  practically  applied  to  Manures. 

The  best  method  of  preparing  the  solution  of  the  manure  is  to  heat  10  Gm. 
to  dull  redness  for  15  minutes,  and  when  cold  to  reduce  it  to  a  fine  powder 
in  a  mortar,  and  add  gradually  10  Gm.  of  sulphuric  acid  diluted  to  200  Cc. 
with  water.  Rinse  the  whole  into  a  stoppered  bottle,  and  make  up  with 
water  to  i  liter.  Shake  up  occasionally  for  an  hour,  and  having  then  let 
all  settle  for  three  hours,  draw  off  100  Cc.  (=  i  Gm.  manure)  for  analysis. 
To  this  add  a  little  citric  acid  (10  drops  of  a  cold  saturated  solution), 
followed  by  a  slight  excess  of  ammonium  hydrate.  Again  acidify  with  acetic 
acid,  add  10  Cc.  sodium  acetate  solution,  and  then  use  the  uranic  solution  as 
usual.  If  all  these  quantities  be  rigorously  adhered  to;  each  Cc.  of  uranic 
solution  used  can  without  further  calculation  be  taken  as  indicating  i  per  cent, 
of  tricalcium  phosphate  in  the  manure. 

This  process  is  highly  recommended  by  Mr.  Sutton,  of  Norwich,  and 
elaborate  details  will  be  found  in  his  work  on  Volumetric  Analysis. 

XIII.    STANDARD   SOLUTION    OF   BARIUM   CHLORIDE. 

Normal  —  103 '82  Gm.  per  1000  Cc.  of  BaCl^. 

This  is  used  for  taking  the  amount  of  a  soluble  sulphate,  by  adding  it  to  a 
known  weight  of  the  sulphate  dissolved  in  water  acidulated  with  hydrochloric 
acid,  until  precipitation  ceases.  The  process,  however,  is  tedious,  and  the 
end  of  the  reaction  is  not  sharp,  and  it  is  therefore  rarely  employed.  The 
following  is  a  specimen  of  the  reaction,  using  magnesium  sulphate  : — 

MgSO4  .  7H2O  +  BaCl2  =  BaSO4  +  MgCl2  +  7H2O. 
Each  Cc.  of  the  standard  solution  equals  '03993  SOs  or  '04791  SO4. 

The  solution  is  made  by  dissolving  103*82  Gm.  of  pure  barium  chloride  dried 
at  104°  C.  in  i  liter  of  water. 


XIV.   STANDARD   MAYER'S   SOLUTION. 

Made  by  dissolving  13*546  Gm.  of  pure  mercuric  chloride  and  49*8  Gm. 
of  potassium  iodide  in  water,  and  then  making  up  to  1000  Cc. 

This  solution  is  used  for  the  estimation  of  alkaloids,  which  should  be  free 
from  any  mucilaginous  matter  and  preferably  dissolved  in  a  little  dilute 
sulphuric  acid.  The  reagent  is  added  till  precipitation  ceases,  and  the  exact 
equivalent  for  each  alkaloid  should  be  practically  checked  by  operating  on 
a  known  weight  of  the  pure  alkaloid,  and  then  always  using  the  solution 
under  exactly  the  same  conditions  in  future  analysis.  In  the  author's  hands 
the  process  has  not  worked  very  well,  except  for  the  amount  of  emetine  in 
ipecacuanha,  which  may  be  rapidly  ascertained  as  follows : — 

15  Gm.  of  ipecacuanha  are  treated  -with  1-5  Cc.  of  dilute  sulphuric  acid, 
and  sufficient  alcohol  of  80  per  cent,  added  to  make  the  whole  bulk  up 
to  150  Cc.  The  whole  is  allowed  to  stand  for  24  hours,  and  100  Cc.  are 
decanted  off  for  analysis.  The  liquid  is  evaporated  until  all  the  alcohol  is 
driven  off,  and  then  brought  under  the  burette  containing  the  test  solution, 
which  is  run  in  until  it  ceases  to  give  a  precipitate.  The  final  point  of  the 
reaction  is  ascertained  by  filtering  off  a  drop  or  two  in  a  watch-glass  placed 
on  black  paper,  and  adding  a  drop  of  the  reagent,  when,  if  no  cloudiness 
appears,  the  precipitation  of  the  alkaloid  is  complete.  The  number  of  Cc. 
of  the  test  used  multiplied  by  -0189  gives  the  amount  of  alkaloid  in  10  Gm.  of 
the  sample,  which  again  multiplied  by  10  gives  percentage. 


ANALYSIS  BY  THE  NITROMETER. 


133 


XV.   ANALYSIS   BY   THE   NITROMETER. 

(A)  General  Remarks. 

This  useful  instrument  is  illustrated  in  fig.  29.  It  consists  of  a  measuring 
tube  (A)  graduated  in  Cc.,  having  a  funnel-shaped  cup  (c)  connected  to  it 
by  means  of  the  stopcock  (D).  This  cock  is  a  "three-way"  one,  and 
according  to  the  direction  in  which  it  is  turned,  it  can  make  connection 
and  discharge  the  contents  of  the  cup  either  into  the  tube  A  or  out  in 
the  waste  opening  at  E;  or  it  can  make,  or  quite  shut  off,  all  connection 
between  A  and  the  outer  air  through  E.  Connected  to  A  by  a  piece  of 
flexible  indiarubber  tube  is  the  ungraduated  control  tube  B.  The  object  of 
the  apparatus  is  the  rapid  and  accurate  measurement,  at  definite  temperature 
and  pressure,  of  gases  evolved  during  any  reaction;  and  it  takes  its  name 
from  the  fact  that  it  was  first  used  to  measure  the  nitric  c 
oxide  given  off  by  the  decomposition  of  nitric  acid.  If  we 
fill  the  instrument  with  a  fluid  (say  mercury)  right  up  to 
the  tap,  and  having  closed  the  tap  D,  we  lower  the  tube  B 
and  admit  a  little  air  through  E  (by  opening  and  again 
closing  the  tap),  we  will  have  a  volume  of  gas  in  the 
measuring  tube  which  we  desire  to  measure  under  definite 
conditions.  Then  (i)  by  allowing  the  instrument  to  stand 
until  its  contents  must  have  assumed  the  temperature  of 
the  room,  a  thermometer  suspended  to  the  stand  will  give 
the  temperature  of  the  gas.  (2)  By  then  raising  or  lowering 
the  control  tube  (B),  so  that  the  level  of  the  liquid  both  in 
it  and  in  the  measuring  tube  is  the  same,  it  is  evident  that 
the  pressure  inside  A  is  the  same  as  in  the  room,  and 
reference  to  a  barometer  standing  near  will  give  that  pres- 
sure. It  now  only  remains  to  read  off  the  volume  of  the 
gas  in  the  measuring  tube,  and  having  corrected  it  to  N.T.P.  (see  page  101), 
to  calculate  its  weight  in  Gm.  from  its  volume  in  Cc.,  by  multiplying  the 
number  of  Cc.  of  volume  at  N.T.P.  by  the  weight  of  i  Cc.  of  the  gas  in 
Gm.  This  latter  is  obtained  by  multiplying  '0896  Gm.  by  /iaJ/the  molecular 
weight  of  the  gas,  and  then  dividing  by  1000.  Suppose,  for  example,  that 
we  have  obtained  20  Cc.  of  nitric  oxide  at  15°  C.  and  750  Mm.  barometer, 
and  we  require  to  know  the  weight  of  NO  so  got,  we  should  say  :  — 

7*20  =  IS'788  Co.,  corrected  volume  at  N.T.P. 


Fig.  29. 


(•) 


-  — 


=  '001344  Gm.,  weight  of  I  Cc.  NO. 
(c)  18788  X  '001344  =  -0253  Gm.,  weight  of  NO  found. 

The  various  possible  applications  of  this  instrument  are  so  numerous  that 
exhaustive  details  would  be  impossible  in  the  present  work  ;  but  the  following 
should  be  practised  as  typical  instances  of  its  use  :  — 


(B)  Estimation  of  the  Strength  of  Spirit  of  Nitrous  Ether. 

The  active  principle  of  this  drug  is  ethyl  nitrite.  Nitrites  when  mixed 
with  excess  of  potassium  iodide  and  acidulated  with  sulphuric  acid  cause 
a  liberation  of  iodine,  and  evolve  all  their  nitrogen  in  the  form  of  nitric  oxide, 
thus  :— 

C2H5.NO2  +  KI  +  H2SO4  =  C2H5.HO  +  KHSO4  +  I  +  NO. 
The  process   is  thus  conducted.     The  nitrometer  is  filled  with  saturated 
solution  of  sodium  chloride,  with  which,  owing  to  its  density,  a  strong  spirit 


134  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

will  not  readily  mix.  We  then  put  about  30  Gm.  of  the  spirit  of  nitrous 
ether,  which  has  been  previously  shaken  with  0*5  Gm.  of  potassium  bicar- 
bonate, into  a  tared  100  Cc.  measuring  flask,  and  weigh  accurately.  Add 
sufficient  alcohol  to  bring  the  volume  to  exactly  100  Cc.  Introduce  into  a 
nitrometer  10  Cc.  of  this  alcoholic  solution,  followed  by  10  Cc.  of  potassium 
iodide,  and  afterwards  by  10  Cc.  of  normal  sulphuric  acid.  When  the  volume 
of  gas  has  become  constant  (within  30  to  60  minutes),  read  it  off.  Multiply 
this  volume  in  Cc.  by  0-307,  and  divide  the  product  by  the  original  weight 
of  the  spirit  of  nitrous  ether.  At  standard  temperature  and  pressure,  the 
quotient  will  represent  the  percentage  of  ethyl  nitrite  in  the  liquid,  which 
should  not  be  less  than  4  per  cent.  The  temperature  correction  is  one-third 
of  i  per  cent,  of  the  total  percentage  just  found  for  each  degree,  additive  if 
temperature  is  below,  subtractive  if  above,  25°  C.  (77°  F.).  The  barometric 
correction  is  four-thirtieths  of  i  per  cent,  for  each  millimeter,  additive  if 
above,  subtractive  if  below,  760. 

(C)  Estimation  of  the  Strength  of  Amyl  Nitrite. 

Start  with  about  3  Cc.  of  amyl  nitrite,  and  having  proceeded  exactly  as 
for  sp.  cetheris  nit.,  multiply  the  volume  of  gas  obtained  in  Cc.  by  4*8  and 
divide  by  the  original  weight  of  amyl  nitrite  taken.  The  sample  should  not 
show  less  than  80  per  cent. 

(Z>)  Estimation  of  Nitric  Acid  in  Nitrates. 

This  depends  on  the  fact  that  when  a  nitrate  is  shaken  up  with  excess  of 
sulphuric  acid  and  mercury  the  following  reaction  takes  place  :  — 


2KN03  +  4H2S04  +  3Hg  =  3HgS04  +  K2SO4  +  2NO  +  4H2O- 

thus  showing  that  each  molecule  of  the  nitrate  radical  gives  off  a  molecule  of 
NO.  If  any  chlorides  or  other  haloid  salts  be  present,  they  are  first  removed 
by  adding  a  slight  excess  of  argentic  sulphate  to  the  solution  and  filtering. 
No  quantity  of  A  nitrate  exceeding  2  Decigm.  should  be  used,  other- 
wise more  gas  may  be  evolved  than  the  instrument  will  conveniently  hold. 
The  nitrometer  is  charged  with  mercury,  and  the  nitrate  solution,  which 
should  not  exceed  5  Cc.,  is  put  into  the  cup  and  passed  therefrom  into 
the  measuring  tube,  followed  by  excess  of  strong  sulphuric  acid.  The 
instrument  is  well  agitated  for  some  time,  and  when  action  has  ceased 
and  the  contents  have  cooled  down  to  the  temperature  of  the  room,  the 
level  is  adjusted  and  the  volume  of  NO  read  off  and  calculated.  All  the 
precautions  already  mentioned  must  be  observed.  If  any  nitrites  be  present, 
they  affect  the  accuracy  of  the  estimation,  being  also  decomposed  to  nitric  oxide. 

(E)  Estimation  of  Soluble  Carbonate. 

It  has  been  proposed  to  use  the  nitrometer  for  taking  the  strength  of  the 
medicinal  solution  of  ammonium  carbonate  in  the  spirit  known  as  spiritus 
ammonia  aromaticus.  A  given  volume  of  the  spirit  is  placed  in  the  cup  and 
introduced  into  the  nitrometer  charged  with  mercury.  This  is  followed  by 
an  excess  of  dilute  hydrochloric  acid,  and  the  carbon  dioxide  evolved  by  the 
action  of  the  acid  upon  the  carbonate  is  measured.  The  percentage  of 
ammonium  carbonate  may  then  be  calculated,  or  an  empirical  comparison  of 
volume  on  the  principle  of  that  already  described  for  spirit  of  nitrous  ether 
may  be  applied.  According  to  Mr.  Gravill,  the  originator  of  the  test,  good 


ANALYSIS  BY  THE  NITROMETER.  135 

aromatic  spirit  of  ammonia  should  give  off  seven  times  its  volume  of  carbon 
dioxide  after  allowing  a  correction  for  the  slight  solubility  of  the  gas  in  the 
liquid  with  which  it  is  inclosed. 

(F)  Estimation  of  the  Strength  of  Solutions  of  Hydrogen  Peroxide. 

This  depends  upon  the  fact  that,  when  hydrogen  peroxide  acts  upore 
potassium  permanganate,  acidulated  with  sulphuric  acid,  oxygen  is  evolved* 
One  half  of  this  oxygen  is  due  to  the  peroxide  and  the  other  to  the  perman- 
ganate. The  nitrometer  should  be  charged  with  concentrated  solution  of 
sodium  sulphate  (the  B.P.  uses  brine),  and  i  Cc.  of  the  solution  introduced 
from  the  cup,  followed  by  12  Cc.  of  a  mixture  of  i  Cc.  H2SO4,  2  Cc.  of  5  per 
cent,  solution  of  K2Mn2O8  and  7  Cc.  H2O.  The  contents  of  the  measuring 
tube,  after  the  reaction  is  complete,  must  remain  colored  violet,  thus  showing 
that  sufficient  permanganate  has  been  employed.  B.P.  solution  of  hydrogen 
peroxide  should,  when  thus  treated,  give  not  less  than  18  and  not  more  than. 
22  times  its  volume  of  oxygen. 

(G)  Estimation  of  Urea  in  TJrine. 

This  process  depends  on  the  fact  that  when  urea  is  decomposed  by  an 
alkaline  hypobromite  or  hypochlorite,  it  gives  off  its  nitrogen  in  the  free  state, 
the  following  reaction  taking  place  :  — 

N2H4CO  +  sNaBrO  =  sNaBr  +  N2  +  CO2  +  2H2O. 


A  small  flask  is  fitted  with  a  tight  cork,  through  which  passes  a  funnel' 
tube  closed  by  a  clamp  and  reaching  to  the  bottom  of  the  flask,  and  also 
a  bent  delivery  tube  just  passing  through  the  cork.  5  Cc.  of  the  urine  is- 
placed  in  this  flask,  and  the  nitrometer  having  been  filled  with  water  the  flask- 
is  attached  to  the  tap  of  the  nitrometer  at  the  end  E  (see  fig.  29,  page  133). 
20  Cc.  of  a  solution  of  bromine  in  sodium  hydrate  solution  is  then  placed 
in  the  funnel  and  allowed  to  run  into  the  urine,  and  the  clamp  immediately 
closed.  At  the  same  moment  the  tap  of  the  nitrometer  is  so  placed  as  to 
establish  connection  between  E  and  the  measuring  tube.  A  little  warm  water 
in  a  basin  is  applied  to  the  flask  to  hasten  the  reaction,  and  when  no  more 
gas  is  evolved,  the  tap  is  closed,  the  temperature  and  pressure  adjusted,  and 
the  volume  read  off  as  usual.  Each  Cc.  of  gas  at  N.T.P.  represents  '0029 
Gm.  of  urea  present  in  the  5  Cc.  of  urine  acted  upon. 

Fig.  29*2  represents  a  very  simple  apparatus  that  can  be  improvised  in  a 
shop  or  dispensary.  5  Cc.  of  urine  are  placed  in  the  test  tube  (A),  and  20  Cc.. 
of  hypobromite  solution  (or  strong  liquor 
sodcz  chlorinate  will  do  as  well)  into  the 
bottle  B.  The  bottle  c  is  filled  with 
water,  and  its  delivery  tube  is  suspended 
in  a  graduated  Cc.  measure.  When  all 
is  tight  the  urine  is  caused  to  mix  with 
the  reagent  by  tipping  up  B,  and  the  gas 
produced  passing  into  c  displaces  water, 
which  latter  runs  into  the  measure.  The 
number  of  Cc.  of  water  thus  collected  in 

the  measure  multiplied  by  '058  gives  the  percentage  01  urea  in  the  urine.  It 
is  manifest  that  i  fluid  dram  may  be  taken,  and  the  measure  used  may  be  an 
ordinary  2  oz.  dispensing  one  (where  only  English  weights  and  measures  are 
handy),  when  each  fluid  dram  of  water  in  the  measure  at  the  finish  will  equal 
•29  per  cent,  of  urea. 


136  VOLUMETRIC  QUANTITATIVE  ANALYSIS. 

XVI.   COLORIMETRIC  ANALYSIS. 
General  Remarks. 

This  is  a  variety  of  volumetric  analysis  in  which  the  amount  of  a  substance 
present  in  solution  is  found  by  adding,  to  a  given  volume,  a  fixed  quantity  of 
a  reagent  and  observing  the  color  produced.  This  color  is  then  matched 
by  adding,  to  an  equal  volume  of  distilled  water,  the  same  mixed  quantity  of 
reagent,  and  running  in  a  volumetric  solution  of  the  pure  substance  until  the 
same  tint  is  produced.  Evidently  when  this  point  is  reached  the  amount  of 
substance  present  in  the  solution  under  analysis  equals  that  in  the  volumetric 
solution  used  for  the  comparative  experiment.  The  applications  commonly 
occurring  of  this  method  are  : — 

(A)  Estimation  of  Ammonia  by  "  Nesslerizing." 

For  this  process  the  following  solutions  and  apparatus  are  required : — 

(a)  NessleSs  solution.     Dissolve  35  parts  of  potassium  iodide  in  100 

parts  of  water.  Dissolve  17  parts  of  mercuric  chloride  in  300 
parts  of  water.  The  liquids  may  be  heated  to  aid  solution,  but 
if  so  must  be  cooled.  Add  the  latter  solution  to  the  former 
until  a  permanent  precipitate  is  produced.  Then  dilute  with  a 
20  per  cent,  solution  of  sodium  hydrate  to  1000  parts;  add 
mercuric  chloride  solution  until  a  permanent  precipitate  again 
forms  ;  allow  to  stand  till  settled,  and  decant  off  the  clear 
solution.  The  bulk  should  be  kept  in  an  accurately  stoppered 
bottle,  and  a  quantity  transferred  from  time  to  time  to  a  small 
bottle  for  use.  The  solution  improves  by  keeping. 

(b)  Standard  ammonia  solution.     Dissolve  3*15  Gm.  pure  ammonium 

chloride  in  1000  Cc.  of  distilled  water  free  from  ammonia. 
For  use,  dilute  10  Cc.  of  this  solution  to  1000  Cc.  with  ammonia 
free  distilled  water.  Each  Cc.  of  the  diluted  solution  will  then 
contain  *oi  Milligm.  of  NHs  (i.e.  "ooooi  Gm.). 

(c)  Two  narrow  cylinders  of  colorless  glass,  of  perfectly  equal  height 

and  diameter,  holding  about  70  Cc.,  and  graduated  at  50  Cc. 
These  should  either  have  a  milk  glass  foot  or  should  stand 
upon  a  perfectly  white  paper. 

(d)  A  pipette  to  deliver  2  Cc. 

(e)  A  quantity  of  ammonia-free  distilled  water.     This  is  obtained  by 

placing  a  liter  of  ordinary  distilled  water  in  a  retort,  attaching 
a  condenser  and  distilling  until  what  passes  over  ceases  to  give 
any  color  with  "  Nessler's  solution."  The  remaining  water  in 
the  retort  is  then  cooled  and  bottled  for  use. 

The  liquid  in  which  ammonia  is  to  be  estimated  (usually  a  distillate  obtained 
in  water  analysis)  is  first  made  up  to  a  fixed  bulk  with  ammonia-free  distilled 
water,  and  the  bulk  noted.  It  must  be  so  diluted  that  it  only  gives  a  color 
and  not  a  precipitate  with  "Nessler."  50  Cc.  of  this  solution  are  placed  in  a 
cylinder,  and  2  Cc.  of  "Nessler"  having  been  added  by  the  pipette,  and  the 
whole  stirred  with  a  perfectly  clean  rod,  the  color  produced  is  observed.  A 
little  experience  soon  teaches  the  operator  to  judge  the  probable  amount  of 
ammonia  solution  required  to  produce  a  similar  tint.  Let  us  suppose,  for 
example,  that  the  color  is  judged  to  be  equal  to  2  Cc.  of  ammonia,  then  we 
proceed  to  confirm  our  idea :  2  Cc.  of  the  standard  ammonia  solution  are  run 
from  a  burette  into  the  other  cylinder,  ammonia-free  water  is  added  to  50  Cc., 


COL ORIMETRIC  ANAL  YSIS.  137 

then  the  2  Cc.  of  "  Nessler,"  and  the  whole  stirred  with  the  clean  rod.  If 
now,  after  a  few  minutes,  the  colors  match,  we  are  correct ;  but  if  not,  then 
we  must  try  again  and  again  with  more  or  less  standard  ammonia  until  we  get 
an  exact  match  between  the  colors  in  the  two  cylinders.  This  having  been 
attained,  the  calculation  is  very  simple,  and  will  be  best  explained  by  an 
example.  Suppose  that  we  start  with  a  distillate  containing  ammonia  and 
made  up  to  200  Cc.,  and  that  we  employ  5  Cc.  of  standard  ammonia  solution 
in  the  comparison  experiment,  to  match  the  color  produced  by  "  Nessler  "  in 
50  Cc.  of  such  distillate.  Then  '5  Cc.  x  '01  =  "05,  and  -05  x  4  =  *2  :  there- 
fore the  whole  200  Cc.  of  distillate  contained  "2  Milligm.  of  NH3.  Beginners 
should  train  their  eyes  by  observing  the  colors  produced  by  adding  various 
quantities  of  standard  ammonia  to  50  Cc.  of  ammonia-free  water,  and  then 
introducing  the  "  Nessler."  TV  of  a  Cc.  of  standard  ammonia  will  produce 
a  very  faint  yellow,  while  larger  amounts  will  increase  the  color  to  orange, 
and  finally  to  deep  orange-red.  We  should  always  wait  3  minutes  before 
observing,  as  the  full  color  does  not  appear  under  that  time,  and  the  tem- 
perature of  the  room  should  not  be  below  12°  C. 

(B)  Estimation  of  Nitrites  in  Water. 
See  Water  Analysis,  Chapter  X. 

(C)  Estimation  of  Minute  Quantities  of  Copper  or  Iron. 

This  has  often^to  be  done  in  articles  of  food,  such  as  preserved  vegetables. 
After  having  been  burned,  and  the  ash  dissolved  in  an  appropriate  acid,  a 
solution  is  obtained,  which  is  made  up  to  a  definite  volume.  50  Cc.  is  treated 
with  a  fixed  excess  of  ammonium  hydrate  in  a  "  Nessler  "  glass.  The  same 
amount  of  ammonia  is  added  to  50  Cc.  of  water  in  another  glass,  and  a  very 
weak  standard  solution  of  cupric  sulphate  is  dropped  in  from  a  burette  until 
the  colors  match,  and  the  amount  of  copper  solution  used  is  noted  and 
calculated.  Small  quantities  of  ferric  iron  may  also  be  estimated  in  the  same 
way  by  the  use  of  potassium  ferrocyanide  in  the  presence  of  a  fixed  amount  of 
acidulation  with  hydrochloric  acid,  and  matching  the  color  by  a  weak  stan- 
dard solution  of  ferric  chloride.  This  is  often  useful  in  analyzing  bread  for 
the  presence  of  alum,  when  we  first  weigh  the  precipitate  of  aluminium 
phosphate  containing  some  ferric  phosphate,  then  dissolve  it  in  HC1,  find 
the  amount  of  iron  present  in  this  manner,  and  deduct  it,  so  saving  a  long 
separation. 


CHAPTER   VIII. 

GRAVIMETRIC  QUANTITATIVE  ANALYSIS  OF  METALS 

AND  ACIDS. 


DIVISION    I.    PRELIMINARY    REMARKS. 

GRAVIMETRIC  quantitative  analysis  is  that  method  by  which  the  substance  to 
be  estimated  is  converted  into  some  chemically  definite  compound,  weighed  as 
such,  and  the  amount  of  the  original  substance  obtained  from  this  weight  by 
calculation.  The  same  definite  compound  will  answer  both  for  the  estimation 
of  its  metal  and  of  its  acid.  For  example,  if  we  precipitate  a  known  weight  of 
argentic  nitrate  with  hydrochloric  acid  we  obtain  insoluble  argentic  chloride, 
which  may  be  filtered  out  and  weighed,  and  the  amount  (x)  of  Ag  in  the 
quantity  started  with  calculated  therefrom,  because — 

AgCl  :  Ag        ::  weight  of  AgCl  found  :  x. 
142-3  :  107-11  ::        „  „          „      :  x. 

If,  on  the  other  hand,  we  start  with  a  known  weight  of  hydrochloric  acid, 
precipitate  it  with  argentic  nitrate,  and  collect  and  weigh  the  argentic  chloride 
formed,  we  can  find  the  amount  (x)  of  real  HC1  actually  present  in  quantity- 
started  with,  because — 

AgCl  :  HC1    : :  weight  of  AgCl  found  :  x. 
142-3:36-19::       „  „         „       :x. 

Before  giving  individual  processes  for  quantitative  analysis,  we  must  first 
say  something  about  the  usual  manipulation  involved,  which  will  serve  as 
general  directions,  so  saving  continual  repetition  of  details. 

(A)  The  Preparation  of  Filters. 

Ready-cut  filters  may  be  procured  from  the  dealers  in  chemical  apparatus. 
The  kind  known  as  Swedish  is  the  best  for  all  cases  where  the  precipitate  is 
finely  divided  or  pulverulent.  For  gelatinous  precipitates,  such  as  ferric  hydrate 
and  calcium  phosphate,  the  white  English  or  German  filters  work  more 
rapidly ;  but  they  should  never  be  used,  say,  for  barium  sulphate,  or  calcium 
oxalate,  as  those  bodies  would  very  likely  pass  through  the  pores  of  the  filter, 
and  so  cause  a  loss  in  the  analysis.  Whatever  paper  be  employed,  the  size  for 
quantitative  operations  is,  for  the  larger  sort  six  inches  in  diameter,  for  the 
smaller,  about  two  inches.  The  latter  size  is  used  where  we  have  to  deal 
with  traces  of  precipitate  only,  or  when  a  small  quantity  of  fluid  has  to  be 
filtered.  The  paper  should  yield  nothing  to  dilute  acids,  and  if  the  ash  exceed 
one  milligramme  per  large  filter  it  should  be  reduced  by  placing,  say, 

138 


PRELIMINARY  REMARKS.  139 

100  cut  filters  for  some  hours  in  a  basin  filled  with  a  mixture  of  one  volume 
of  HC1  and  eight  volumes  of  water.  They  must  be  then  repeatedly  washed 
with  distilled  water  till  quite  free  from  acidity,  otherwise  they  woul  J  crumble 
to  pieces  when  being  folded.  The  washing  is  a  very  tedious  operation  indeed, 
and  having  been  completed,  the  basin  is  put  on  to  a  water  bath  till  the  filters 
are  perfectly  dry. 

(B)  Estimation  of  the  Ash  of  Filters. 

This  is  most  conveniently  done  by  folding  ten  filters  in  a  small  compass, 
twisting  a  long  platinum  wire  round  the  packet  so  as  to  form  a  cage,  holding 
the  free  end  in  the  hand  and  the  paper  over  a  previously  weighed  platinum 
crucible,  while  touching  it  with  the  flame  of  a  Bunsen  burner.  The  paper 
burns  and  the  ash  drops  into  the  crucible,  while  any  particles  of  carbon  which 
have  escaped  combustion  are  quite  consumed  by  exposing  the  crucible  foi 
some  time  to  a  red  heat  till  the  ash  gets  perfectly  white.  The  crucible  after 
cooling  is  reweighed,  and  its  increase  is  the  ash  of  ten  filters.  Divided  by  10, 
we  get  the  ash  of  one  filter ;  and  in  every  case  where  both  filter  and  precipitate 
are  burned,  the  ash  of  the  filter  thus  found  must  always  be  deducted  from 
their  total  weight,  and  the  difference  is  then  the  actual  weight  of  the 
precipitate.  Filter  papers  ready  cut  and  freed,  as  far  as  possible,  from  mineral 
matter  by  the  action  of  hydrochloric  and  hydrofluoric  acids  can  now  be 
purchased.  By  the  use  of  such  papers  the  filter  ash  is  so  reduced  that  it  need 
not  be  considered,  except  in  the  most  delicate  investigations. 

(Q  The  CoUection  and  Washing  of  Precipitates. 

When  the  precipitate  has  been  fully  formed  and  the  supernatant  fluid  has 
become  quite  clear,  the  latter  is  poured  on  the  filter  (which  is  either  previously 
tared  or  not,  according  to  circumstances),  care  being  taken  not 
to  disturb  the  precipitate.  This  is  done  by  holding  a  glass  rod 
in  a  perpendicular  position  over  the  filter,  placing  the  lip  of  the 
beaker  against  it,  and  causing  the  liquid  to  flow  steadily  down 
the  rod  into  the  filter.  When  the  latter  is  three-fourths  full,  the 
beaker  is  turned  into  an  erect  position  and  the  rod  drained 
against  the  inside  of  the  lip,  and  then  laid  across  the  top  of  the 
beaker  until  it  is  time  to  refill  the  filter.  After  thus  pouring  off 
as  much  as  practicable,  the  precipitate  remaining  in  the  beaker 
is  treated  with  water  and  well  stirred.  When  the  whole  has  once 
more  settled,  the  clear  fluid  is  again  passed  through  the  filter. 
This  operation  having  been  repeated  three  or  four  times,  the  Fis-  30. 
precipitate  is  allowed  to  pass  on  to  the  filter,  any  particles  which  stick  to 
the  sides  of  the  beaker  being  removed  with  a  feather  or  a  rod  tipped  with  a 
small  piece  of  black  india-rubber  tubing ;  and  the  whole  having  been  thus 
collected,  the  washing  is  continued  by  means  of  a  washing-bottle  (fig.  30),  till 
the  precipitate  is  quite  freed  from  its  soluble  impurities.  For  instance,  in 
estimating  sulphuric  acid,  the  barium  sulphate  is  washed  till  the  filtrate  no 
longer  gives  a  turbidity  with  argentic  nitrate. 

Many  bodies,  as  ferric  and  aluminic  hydrate,  most  phosphates,  barium  sul- 
phate, and  some  of  the  carbonates,  are  best  washed  with  boiling  water.  Others, 
on  the  contrary,  must  be  washed  with  cold  water,  while  a  few  require  washing 
with  special  mixtures — such  as  plumbic  sulphate,  for  which  we  use  cold  water 
acidified  with  some  H.2SO4 ;  magnesium  ammonium  phosphate,  for  which  cold 
dilute  ammonium  hydrate  is  used,  etc. 


140 


-RA  VI METRIC  ANALYSIS   OF  METALS. 


(D)  Drying  of  Precipitates. 

After  the  precipitate  has  been  thoroughly  washed  and  perfectly  drained,  the 
funnel  containing  it  is  loosely  covered  over  with  filter  paper  and  then  put  into 
the  water  oven  or  air  bath  till  dry.  Most  precipitates  are  dried  at  a  temperature 
of  100°  C.  (2i2°F.),  but  some  of  them  require  a  heat  of  105°  C.  (220°  F.)  before 
becoming  constant  in  weight.  Prolonged  and  repeated  drying  is  only  necessary 
when,  the  precipitate  is  weighed  on  the  filter,  as  described  below.  Fig.  31 
shows  a  water  oven  for  drying  at  100°  C.,  while  fig.  32  shows  an  air  bath  for 
drying  at  higher  temperatures.  This  bath  is  fitted  with  an  apparatus  (called 
a  thermostat)  for  automatically  controlling  the  gas  supply,  and  consequently 
the  temperature. 


Fig.  3*. 


(E)  Igniting  and  Weighing  Precipitates. 

Miny  precipitates  must  first  be  ignited  before  they  can  be  weighed.  This 
is  to  drive  off  water,  which  they  may  still  retain  after  drying  at  100°  C.,  or  to 
reduce  them  to  a  more  definite  condition.  For  instance,  zinc  is  best  weighed 
as  oxide,  and  therefore  the  precipitate,  consisting  of  oxycarbonate,  is  first 
ignited.  Iron  is  precipitated  as  hydrate,  but  the  composition  of  that  body  not 
being  constant,  it  is  ignited  and  so  made  into  pure  oxide  before  weighing.  As 
soon,  therefore,  as  the  precipitate  appears  dry,  it  is  carefully  detached  from 
the  filter  and  put  into  a  previously  ignited  and  weighed  crucible,  the  filter  is 
burned  on  the  lid  (which  has  been  weighed  together  with  the  crucible),  the 
ash  is  thrown  into  the  crucible,  and  the  latter  covered  with  the  lid.  The 


Fig.  33- 


Fig.  34- 


crucible  is  now  supported  by  a  pipe-clay  triangle,  and  gently  ignited  at  first, 
to  prevent  spurting  from  the  sudden  evolution  of  steam  or  other  gases.  The 
lid  is  now  taken  off,  and  the  crucible  inclined  a  little,  so  as  to  give  a  free  access 
of  air.  The  ignition  is  continued  for  some  minutes,  and  the  crucible,  having 
been  again  covered  with  a  lid,  is  allowed  to  cool  in  a  desiccator  and  weighed. 
A  desiccator  is  shown  in  fig.  33,  and  will  be  seen  to  consist  of  a  glass  shada 


PRELIMINA  R  Y  REMA  RKS.  ,  ^ , 


in  which  is  a  vessel  containing  strong  sulphuric  acid  to  keep  the  air  under  the 
glass  shade  always  free  from  moisture. 

The  heat  of  an  ordinary  Bunsen  burner  is  generally  sufficient  for  all  pur- 
poses ;  but  the  conversion  of  calcium  carbonate  into  oxide  requires  the  aid  of 
a  gas  blowpipe ;  while  argentic  chloride  must  only  be  heated  over  a  rose 
Bunsen  or  spirit  lamp  until  it  just  begins  to  fuse.  The  filters  are,  as  already 
shown,  burned  separately,  to  prevent  any  reduction  of  the  precipitate  by  the 
carbon  of  the  filter. 

Some  precipitates  are  not  ignited,  but  weighed  on  a  previously  tared  filter. 
Before  weighing  the  filter — for  which  purpose  a  weighing  tube  (fig.  34)  is  used, 
or  the  filter  is  placed  between  two  closely-fitting  watch-glasses  provided  with  a 
clamp  to  hold  them  together — it  must  first  be  dried  for  fifteen  minutes  at 
100°  C.  After  drying  the  precipitate,  the  filter  is  again  placed  in  the  tube  or 
between  the  glasses  and  reweighed :  the  increase  shows,  of  course,  the  weight 
of  the  substance.  It  is  well  to  re-place  the  filter  in  the  bath  for,  say,  half  an 
hour,  and  to  weigh  again.  Should  the  weight  be  considerably  less,  it  must  be 
once  more  put  into  the  bath  and  reweighed.  Another  method  of  weighing 
precipitates  on  a  filter  is  to  prepare  two  filters  of  equal  size,  A  and  B.  Cut  off 
the  bottom  point  of  B,  so  that  A  will  go  inside  it  with  its  point  projecting 
through  the  opening.  Now  put  B  on  the  weight  scale  of  the  balance,  and  cut 
off  minute  slices  from  the  top  of  A  until  the  two  are  exactly  counterbalanced. 
Place  A  inside  B,  and  then,  having  put  both  in  the  funnel,  collect  the  preci- 
pitate, wash  and  dry  as  usual,  and  cool  under  the  desiccator.  Lastly,  detach 
B,  and  use  it  for  a  tare,  putting  it  into  the  weight  pan,  and  then  the  weights 
required  to  balance  A  and  its  contents  will  be  the  weight  of  the  precipitate, 
because,  both  filters  having  been  exposed  to  the  same  conditions,  the  tare  is 
accurate. 

(F}  Estimation  of  Moisture. 

A  watch-glass  is  exactly  tared  on  the  balance,  and  then  2  grammes  of  the 
substance  (in  powder,  if  possible)  are  carefully  weighed  upon  the  glass,  and 
the  total  weight  noted.  The  glass,  with  contents,  is  then  placed  in  the  drying 
oven  and  heated  therein  for  an  hour,  at  the  expiration  of  which  it  is  removed 
to  the  desiccator,  and,  when  cold,  is  weighed  and  the  weight  noted.  It  is 
then  replaced  in  the  oven  for  half-an-hour,  and  the  cooling  and  weighing 
repeated.  If  the  two  weights  do  not  agree  within,  say,  2  milligrammes,  the 
process  is  repeated  until  two  concordant  weighings  are  obtained.  The  weight 
after  drying,  deducted  from  the  total  weight  of  glass  +  substance  started  with, 
gives  the  moisture,  which  figure  multiplied  by  50  gives  percentage. 

(G)  Estimation  of  the  Ash  of  Organic  Bodies. 

This  determination  is  necessary  in  every  analysis  of  a  vegetable  or  animal 
substance.  A  platinum  dish  is  heated  to  redness,  cooled  under  the  desiccator, 
weighed,  and  the  weight  noted.  A  suitable  quantity,  say  5  to  10  grammes  of 
the  substance,  is  weighed  into  the  dish,  which  is  then  arranged  on  a  triangle 
support  over  a  Bunsen  burner  and  heated  to  dull  redness.  If  after  fumes 
cease  the  substance  is  seen  to  have  assumed  a  coke-like  form,  it  is  removed 
from  the  dish  into  a  small,  dry  mortar,  and  having  been  carefully  powdered, 
the  powder  is  replaced  in  the  dish  and  maintained  at  a  dull  red  heat  until  it 
has  become  perfectly  white,  or  at  least  until  all  carbon  has  been  burned  off. 
If  the  burning  proves  very  tedious  and  the  last  traces  of  carbon  are  very 
difficult  to  burn,  the  addition  of  a  light  sprinkling  of  ammonium  nitrate  will 
cause  the  process  to  complete  itself  more  rapidly.  The  dish  is  now  cooled 
under  the  desiccator  and  weighed,  and  the  weight  of  the  empty  dish  having 


142  GRAVIMETRIC  ANALYSIS   OF  METALS. 

been  deducted,  the  difference  gives  the  weight  of  the  ash,  which  is  then  cal- 
culated to  percentage.  The  heat  should  not  be  allowed  to  rise  to  bright 
redness,  because  potassium  and  sodium  chlorides,  which  are  very  common 
constituents  of  the  ash,  would  be  thereby  volatilised  to  some  extent  and  so 
lost.  The  estimation  of  ash  soluble  in  water  is  frequently  of  great  importance 
as  showing,  when  too  low,  that  the  article  has  been  tampered  with  so  as  to 
remove  its  active  properties.  For  example,  tea  which  has  been  used  and 
redried,  or  ginger,  that  has  been  employed  to  make  ginger  essence  and  then 
redried  and  sold  would  both  show  great  deficiency  in  this  respect.  To 
ascertain  the  amount  of  soluble  ash,  the  total  ash  is  extracted  with  boiling 
distilled  water,  filtered,  washed,  and  the  filter  and  contents  having  been  dried 
are  ignited  and  weighed ;  lastly,  this  weight  deducted  from  that  of  the  total 
ash,  gives  the  soluble  ash. 

(ff)  Analytical  Factors  for  Calculating  the  Results  of  Analyses. 

To  save  the  working  out  of  a  rule-of-three  sum  on  the  result  of  each 
analysis  it  is  customary  to  employ  factors.  These  are  obtained  by  dividing 
the  weight  of  the  required  body  by  the  equivalent  weight  of  the  body  in 
the  form  in  which  it  is  precipitated.  Thus,  supposing  we  are  estimating  the 
amount  of  argentic  nitrate  present  in  a  solution  containing  -6  gramme  of  the 
salt,  and  have  precipitated  and  weighed  the  same  in  the  form  of  argentic 
cnloride,  we  have  : — 

Molecular  weight  of  AgNOs   i68'6Q 

Equivalent  weight  of  AgCl  l^J  :  =  l'lS^>  analytical  factor. 
It  now  only  remains  to  multiply  this  factor  by  the  weight  of  the  precipitat- 
to  obtain  the  answer.  Let  us  further  suppose  that  the  weight  of  the  precipie 
tate  was  -5  gramme,  then  1-1854  x  -5  =  -59270  real  AgNO3  present  in  the 
•6  gramme  taken ;  then  5927°  x  ^>  _  ^.^  per  cent  real  ^gNO3  present 
in  the  sample. 


DIVISION  II.    GRAVIMETRIC  ESTIMATION  OF  METALS. 
I.   ESTIMATION   OF  SILVER. 

(A)  As  Argentic  Chloride. 
(Practise  upon  -5  gramme  pure  AgNO3  dissolved  in  100  c.c.  H2O.) 

Silver  is  most  conveniently  weighed  as  chloride.  The  silver  solution  to  be 
estimated  is  acidified  with  nitric  acid,  and  hydrochloric  acid  is  dropped  in 
until  no  more  precipitate  forms.  It  is  best  to  have  the  solution  warm,  and  to 
stir  till  the  supernatant  liquid  has  got  perfectly  clear.  The  clear  fluid  is  now 
poured  off  through  a  filter,  and  the  chloride  is  washed  by  decantation  with 
boiling  water  (always  pouring  the  washings  through  the  filter)  till  every  trace 
of  acid  is  removed,  and  subsequently  the  whole  precipitate  is  brought  upon 
the  filter.  The  filter  and  contents  are  then  dried  in  the  water  oven,  and  the 
chloride  transferred  into  a  weighed  porcelain  crucible,  and  heated  over  a  low 
flame  till  it  just  commences  to  fuse.  The  filter  is  burned  on  the  crucible  lid, 
and  the  ash  treated  with  a  drop  of  aqua  regia,  the  resulting  chloride  dried, 
the  lid  placed  on  the  crucible,  and  the  whole  weighed.  The  tare  of  the 
crucible,  lid  and  filter  ash  having  been  deducted,  the  balance  is  AgCl,  from 
the  quantity  weighed  out  for  analysis. 


ESTIMATION  OF  LEAD  AND  MERCURY.  143 


(ff)  As  Metal. 

(a)  In  organic  salts,  by  igniting  a  weighed  quantity  of  the  salt  in  a  tared 
porcelain  crucible,  and  weighing  the  ash,  which  will  consist  of  pure  metallic 
silver. 

(b)  In  alloys,  by  cupellation,  as  follows :  The  weighed  alloy  is  wrapped  in 
lead  foil,  placed  on  a  little  cup  or  cupel  made  of  bone  ash,  and  heated  to 
bright  redness  in  a  muffle  furnace.     The  lead  oxidises  and  sinks  into  the 
cupel,  carrying  the  impurities  with  it,  and  leaving  a  button  of  pure  silver, 
which  is  cooled  and  weighed. 


8.  ESTIMATION  OF  LEAD. 

(A)  As  Plumbic  Oxide. 

(Practise  upon  '5  gramme  pure  plumbic  acetate.) 

The  solution  containing  the  substance  to  be  analysed  is  precipitated  with 
ammonium  carbonate  in  the  presence  of  a  little  ammonium  hydrate.  The 
precipitated  plumbic  carbonate  is  then  collected  on  a  small  filter,  washed,  and 
dried.  The  dry  precipitate  is  removed  as  completely  as  possible  from  the 
filter-paper,  and  introduced  into  a  weighed  porcelain  crucible.  The  filter 
having  been  burned  on  the  lid,  and  its  ash  added  to  the  contents  of  the 
crucible,  the  whole  is  ignited,  cooled,  and  weighed.  By  ignition  the  oxide 
is  formed ;  and  after  deducting  the  weight  of  the  crucible  and  filter  ash,  the 
balance  is  PbO,  from  the  quantity  weighed  out  for  analysis.  Organic  salts  of 
lead  require  simply  to  be  ignited  in  a  tared  porcelain  crucible,  with  free  access 
of  air,  adding  a  sprinkling  of  ammonium  nitrate  (to  prevent  reduction  to  the 
metallic  state),  and  weighing  the  resulting  PbO. 

(B}  As  Plumbic  Chromate. 

(Practise  upon  "5  gramme  of  plumbic  nitrate.) 

The  solution  is  mixed  with  excess  of  sodium  acetate  and  precipitated  with 
potassium  chromate.  The  precipitate  is  collected,  washed  with  water  acidu- 
lated with  acetic  acid,  dried,  and  ignited  in  a  platinum  crucible  with  the  usual 
precautions.  The  filter  is  burned  on  the  lid,  treated  with  a  drop  or  two  of 
nitric  acid,  dried,  and  again  ignited.  The  crucible  and  contents  are  weighed, 
and  the  tare  of  the  crucible  having  been  deducted,  the  balance  is  PbCrO4, 
from  the  quantity  weighed  out  for  analysis. 

Lead  may  also  be  precipitated  as  PbSO*,  washed  with  cold  and  very  dilutf 
sulphuric  acid,  dried,  ignited,  and  weighed  as  such. 


3.  ESTIMATION  OF  MERCURY. 
(A)  As  Metal. 

(Practise  upon  i  gramme  of  "  white  precipitate,"  which  should  yield  77*5%  Hg.) 

Take  a  combustion  tube  of  hard  glass,  closed  at  one  end,  and  put  in  :  (i)  a 
little  magnesite — MgCO3 ;  (2)  the  weighed  quantity  of  the  mercury  salt,  mixed 
with  excess  of  quicklime  ;  (3)  a  few  inches  of  quicklime  ;  (4)  a  loose  plug  of 
asbestos.  Draw  out  the  open  end  of  the  tube  before  the  blowpipe  and  bend 
it  down  at  a  right  angle.  Give  the  tube  a  tap  or  two  on  the  table  to  insure 


I44  GRAVIMETRIC  ANALYSIS  OF  METALS. 

a  free  passage  along  the  upper  part  for  gases,  and  place  it  in  a  combustion 
furnace,  with  its  open  end  dipping  under  the  surface  of  some  water  in  a  small 
flask.  Heat  the  front  of  the  tube,  and  go  gradually  backwards  until  the  whole 
is  red  hot,  and  the  CO2,  given  off  by  the  MgCO3,  has  swept  all  the  mercury 
vapour  out  of  the  tube.  The  mercury  collects  as  a  globule,  and  is  transferred 
to  a  tared  watch-glass,  perfectly  dried  by  pressure  with  blotting-papar,  and 
weighed.  A  similar  globule  may  be  obtained  by  prolonged  boiling  of  the 
mercury  salt  with  excess  of-stannous  chloride  strongly  acidulated  with  HC1> 
the  flask  used  being  connected  to  an  upright  condenser  to  save  fumes.  With 
HgI2  granulated  copper  must  be  used  instead  of  lime. 

(B]  As  Mercuric  Sulphide. 
(Practise  upon  '5  gramme  of  mercuric  chloride.) 

Through  the  solution  of  the  mercuric  salt  the  current  of  H2S  is  passed  till 
the  liquid  is  saturated.  The  precipitate  is  collected  on  a  weighed  filter, 
washed  first  with  water,  then  with  absolute  alcohol,  and  finally,  to  remove 
any  free  sulphur,  with  a  mixture  of  equal  parts  of  ether  and  carbon  disulphide. 
After  drying  at  100°  C.  and  weighing,  the  balance,  after  deducting  the  tare 
of  the  filter,  is  HgS  from  the  quantity  weighed  out  for  analysis. 

4.  ESTIMATION  OF  CADMIUM. 

As  Sulphide. 
(Practise  upon  -5  gramme  of  CdCO3  dissolved  in  diluted  HC1.) 

The  solution  is  precipitated  with  ammonium  hydrate  and  ammonium  sul- 
phide. The  cadmium  sulphide  is  collected  in  a  weighed  filter,  washed,  dried 
at  100°  C.,  and  weighed  as  CdS.  In  the  presence  of  metals  of  the  fourth 
group  the  solution  must  be  slightly  acidified  with  hydrochloric  acid  and 
precipitated  by  a  current  of  sulphuretted  hydrogen. 

5.  ESTIMATION  OF  COPPER. 

(A)  As  Cupric  Oxide. 
(Practise  upon  -5  gramme  of  pure  CuSO*  .  5H2O.) 

The  solution  is  boiled  with  a  slight  excess  of  sodium  hydrate.  The 
precipitate  is  filtered  out,  washed,  and  dried.  It  is  then  carefully  removed 
from  the  paper  to  a  weighed  crucible,  and  the  filter  having  been  burned  on 
the  lid  and  the  ash  added  to  the  contents  of  the  crucible,  the  whole  is  well 
ignited,  cooled  in  a  desiccator,  and  weighed  rapidly,  because  cupric  oxide  is 
very  hygroscopic.  To  make  sure  that  the  oxide  contains  no  cuprous  oxide,  it 
is  moistened  with  a  little  fuming  nitric  acid,  dried  with  the  lid  on,  ignited 
for  ten  minutes,  and  then  weighed  as  CuO.  This  operation  requires  care, 
being  liable  to  involve  loss  by  spurting. 

(£)  As  Metallic  Copper. 

The  solution,  which  must  be  free  from  other  metals  precipitable  by  electro- 
lysis, is  introduced  into  a  weighed  and  very  clean  platinum  basin.  It  must 
contain  a  slight  excess  of  sulphuric  acid,  but  on  no  account  nitric  acid.  The 
dish  is  then  attached  to  the  wire  from  the  zinc  plate  of  a  galvanic  cell,  thus 
becoming  the  cathode.  The  other  wire  is  connected  to  a  piece  of  platinum 


ESTIMATION  OF  BISMUTH,   GOLD,  PLATINUM,  AND    TIN.     1^5 

wire  to  form  an  anode,  and  this  latter  is  then  immersed  in  the  liquid.  After  a 
short  time  the  fluid  will  become  quite  colourless,  and  the  basin  will  be  coated 
with  metallic  copper.  The  fluid  is  now  poured  off,  and  the  copper  repeatedly 
washed  with  boiling  water  till  all  acidity  is  removed.  The  basin  is  finally 
rinsed  with  absolute  alcohol,  quickly  dried,  weighed,  and  the  tare  of  the  basin 
having  been  deducted,  the  difference  is  metallic  copper  in  the  quantity 
weighed  out  for  analysis. 

The  use  of  a  battery  may  be  dispensed  with,  and  a  fragment  of  pure  zinc 
used  to  precipitate  the  copper,  with  sufficient  acid  to  dissolve  all  the  zinc 
before  pouring  off. 

6.  ESTIMATION  OF  BISMUTH. 

(A)  As  Bismuth  Sulphide. 
(Practise  upon  75  gramme  of  bismuthi  et  ammonia  citras  B.P.) 

This  process  (although  employed  in  the  B.P.)  cannot  be  much  recom- 
mended, as  the  sulphide  is  apt  to  increase  in  weight  on  drying,  owing  to  the 
absorption  of  oxygen.  A  current  of  sulphuretted  hydrogen  is  passed  through 
the  acid  bismuth  solution ;  the  resulting  sulphide  is  collected  on  a  tared  filter, 
dried  at  100°  C.,  and  weighed  as  BigSg. 

(B)  As  Bismuth  Oxide. 

The  solution  for  analysis  is  diluted  with  water,  and  precipitated  with  a 
slight  excess  of  ammonium  carbonate.  The  precipitated  bismuthous  oxy- 
carbonate  is  collected,  washed,  and  dried.  It  is  then  separated  from  the  filter 
paper,  and  the  latter  having  been  burned  on  the  lid  of  a  weighed  crucible, 
the  whole  is  introduced  into  the  crucible,  and  ignited,  cooled,  and  weighed  as 
Bi208. 

7.  ESTIMATION  OF  GOLD. 
As  Metallic  Gold,  by  Cupellation. 

The  alloy  containing  the  gold  is  treated  exactly  as  described  under  silver. 
The  resulting  metallic  button  is  rolled  out  into  a  flat  foil,  and  is  then  digested 
with  nitric  acid,  which  dissolves  any  silver,  and  the  resulting  gold  is  re-fused 
into  a  button  and  weighed. 

8.  ESTIMATION  OF  PLATINUM. 
As  Metallic  Platinum. 

The  solution,  which  must  contain  the  platinum  as  chloride,  is  concentrated 
and  precipitated  with  excess  of  ammonium  chloride.  The  precipitate  is  well 
washed  with  rectified  spirit,  dried,  ignited,  and  weighed  as  metallic  platinum. 

9.  ESTIMATION  OF  TIN. 

(A)  As  Stannic  Oxide. 

Alloys  containing  tin,  but  free  from  antimony  or  arsenic,  are  treated  with 
nitric  acid,  which  converts  the  tin  into  oxide  and  other  metals  into  nitrates. 
The  acid  fluid  is  evaporated  nearly  to  dryness,  the  residue  taken  up  with 

10 


146  GRAVIMETRIC  ANALYSIS  OF  METALS. 

water  and  a  little  nitric  acid ;  the  oxide  is  washed  by  decantation,  collected 
on  a  filter,  completely  washed  and  dried.  It  is  then  as  completely  as  possible 
detached  from  the  filter,  the  latter  is  burned  on  a  lid,  the  ash  added  to  the 
contents  of  the  crucible,  and  the  whole  ignited.  After  cooling,  the  oxide  is 
moistened  with  a  little  nitric  acid,  dried  (with  the  lid  on),  again  ignited,  and 
weighed  as  SnO2. 

Where  we  have  to  deal  with  tin  in  solution,  the  following  method  is 
applied : — 

The  solution,  which  must  be  free  from  other  metals  of  the  first  three  groups, 
is  precipitated  with  sulphuretted  hydrogen,  the  resulting  sulphide  is  washed 
with  solution  of  ammonium  acetate,  which  will  prevent  the  stannic  sulphide 
from  passing  through  the  filter.  The  sulphide  is  transferred  to  a  weighed 
crucible,  and  the  whole  ignited,  at  first  very  gently,  until  fumes  of  sulphurous 
anhydride  cease,  and  then  at  a  very  high  temperature,  with  the  addition  of  a 
fragment  of  ammonium  carbonate. 

This  process  depends  on  the  conversion  of  the  sulphide  into  SnO2  by 
ignition ;  but  it  must  be  conducted  with  care,  as  a  too  rapid  application  of 
heat  would  cause  the  change  to  take  place  suddenly,  and  some  of  the  sulphide 
wouM  be  lost. 

(B)  As  Metallic  Tin. 

This  process,  which  is  only  applicable  to  tin  stone,  consists  in  fusing  a 
known  quantity  of  the  pulverised  ore  with  potassium  cyanide  in  a  porcelain 
crucible,  when  a  small  button  or  granules  of  metallic  tin  will  be  obtained  on 
treating  the  mass  with  water.  The  tin  is  washed,  dried,  and  weighed. 


10.  ESTIMATION  OF  ANTIMONY. 

As  Antimonious  Sulphide,  with  or  without  Subsequent  Conversion  into 
Antimonious  Antimonic  Oxide. 

(Practise  upon  '5  gramme  of  "  tartar  emetic.") 

The  acid  solution  is  mixed  with  tartaric  acid,  to  prevent  the  precipitation  of 
an  oxysalt,  diluted  with  water,  and  precipitated  with  sulphuretted  hydrogen, 
the  sulphide  collected  on  a  weighed  filter,  dried  at  105°  C.,  and  weighed. 
The  conversion  of  the  sulphide  into  oxide  is  best  done  by  igniting  an  aliquot 
part  in  a  porcelain  crucible,  with  excess  of  mercuric  oxide,  and  finally  igniting 
very  strongly.  The  remaining  Sb2O4  is  then  weighed.  The  B.P.  simply 
moistens  and  warms  the  sulphide  with  nitric  acid  till  red  fumes  cease,  and 
then  dries,  ignites,  and  weighs  as  Sb2O4. 


11.  ESTIMATION  OF  ARSENIC. 

(A)  As  Arsenious  Sulphide. 

(Practise  upon  '5  gramme  As2O3.) 

The  folution  must  contain  the  arsenic  as  arsenious  acid.  After  adding 
some  HO,  a  current  of  sulphuretted  hydrogen  is  passed  through  the  liquid, 
till  the  latter  acquires  a  strong  smell.  The  excess  of  gas  is  now  removed  by 
warming  the  fluid  and  passing  a  current  of  carbonic  anhydride  through  it. 
The  sulphide  is  collected  on  a  weighed  filter,  washed,  dried  at  100°  C.,  and 
weighed  as  As2S3. 


ESTIMATION  OF  COBALT,   NICKEL,   AND  MANGANESE,     147 


(B)  As  Magnesium  Ammonium  Arseniate. 

If  the  substance  be  arsenious  acid  it  is  dissolved  in  some  hot  solution  of 
sodium  carbonate,  excess  of  hydrochloric  acid  is  added,  and  the  fluid  mixed 
with  excess  of  bromine  water.  Arsenic  and  sulphur  compounds,  on  the  other 
hand,  are  dissolved  in  hot  potassium  hydrate  and  treated  with  excess  of 
chlorine  gas  to  convert  them  into  arsenic  acid.  The  solution  of  arsenic  acid 
thus  obtained  by  either  of  the  foregoing  methods  is  mixed  with  large  excess 
of  ammonium  hydrate,  and,  after  being  allowed  to  cool,  precipitated  with 
magnesia  mixture.  After  standing  for  at  least  twelve  hours,  the  precipitate 
is  collected  on  a  weighed  filter,  washed  with  a  mixture  of  one  volume  of 
ammonium  hydrate  and  three  volumes  of  water  till  free  from  chlorine,  dried 
for  three  hours  at  105°  C.,  and  weighed  as  (MgNH4AsO4)2  H2O. 


12.  ESTIMATION  OF  COBALT. 

As  Potassium  Cobaltous  Nitrite. 

The  solution  is  concentrated  to  a  small  bulk,  the  excess  of  acid  is  neutralised 
with  potash,  and  excess  of  potassium  nitrite  and  a  little  acetic  acid  (to  keep 
the  solution  slightly  acid  to  test-paper)  are  then  added.  After  the  lapse  of 
twenty-four  hours  all  the  cobalt  will  have  crystallised  out  as  potassium  cobaltous 
nitrite.  This  salt  is  quite  insoluble  in  the  mother  liquor,  but  slightly  so  in 
pure  water.  For  the  washing  a  10%  solution  of  potassium  acetate  is  used, 
wherein  the  salt  is  also  insoluble,  and  the  acetate  is  afterwards  removed  by 
washing  with  alcohol.  A  weighed  filter  is  used  and  the  precipitate  dried  at 
100°  C. 

13.  ESTIMATION  OF  NICKEL. 

As  Metal. 

The  solution  is  precipitated  with  excess  of  sodium  hydrate  and  boiled. 
The  precipitate  is  washed  with  boiling  water,  dried,  ignited,  and  weighed. 
The  ignited  residue,  or  a  known  portion  of  it,  is  now  introduced  into  a 
weighed  porcelain  boat,  and  reduced  at  red  heat  by  a  current  of  hydrogen. 
The  reduced  metallic  nickel  is  afterwards  weighed. 


14.  ESTIMATION  OF  MANGANESE, 
As  Manganese-manganic  Oxide. 

(Practise  upon  75  gramme  of  pure  MnS04  •  7H<,O.) 

The  solution  for  analysis,  if  strongly  acid,  is  neutralised  with  ammonium 
hydrate  and  precipitated  by  ammonium  sulphide.  The  precipitated  manganous 
sulphide  is  washed  with  water  containing  ammonium  sulphide,  and  dissolved 
in  hydrochloric  acid.  Excess  of  sodium  acetate  is  then  added,  and  chlorine 
gas  is  passed  through  the  liquid  until  all  the  manganese  precipitates  as 
manganic  peroxide,  which  is  then  collected,  washed,  and  calcined  in  a 
weighed  crucible  to  bright  redness.  This  forms  Mn3O4;  the  crucible  with 
the  contents  is  then  cooled  and  weighed. 


148  GRAVIMETRIC  ANALYSIS   OF  METALS. 

15.  ESTIMATION  OF  ZINC. 

As  Zinc  Oxide. 

(Practise  upon  75  gramme  of  pure  ZnSC>4  •  7H2O.) 

The  solution  of  the  zinc  salt  is  precipitated,  while  boiling,  with  sodium 
carbonate,  and  the  whole  is  well  boiled.  The  precipitate  is  allowed  to  settle, 
washed  by  decantation  wi  h  boiling  water,  filtered  out,  and  dried.  It  is  then 
introduced  into  a  weighed  crucible,  ignited  for  some  time  at  a  bright  red 
heat,  cooled,  and  weighed.  The  ignition  changes  the  precipitated  zinc 
carbonate  to  oxide,  and  it  is  weighed  as  ZnO.  Or  the  solution  is  precipitated 
with  ammonium  sulphide,  the  zinc  sulphide  collected  on  a  filter,  washed  with 
dilute  ammonium  sulphide,  dried,  ignited,  and  finally  weighed  as  oxide. 
This  latter  method  is  useful  when  only  small  quantities  of  zinc  are  present. 

16.  ESTIMATION  OF  IRON. 

As  Ferric  Oxide. 

(Practise  upon  "75  gramme  of  pure  FeSC>4  •  7H2O.) 

The  solution  is  boiled  with  a  nitro-hydrochloric  acid,  to  ensure  that  the 
whole  of  the  iron  is  in  the  ferric  state.  Excess  of  ammonium  hydrate  is 
added,  the  whole  boiled  and  rapidly  filtered.  The  precipitated  ferric  hydrate 
is  washed  with  boiling  water,  dried,  and  ignited  in  a  weighed  crucible  for  some 
time. 

In  the  presence  of  organic  matter,  such  as  citric  or  tartaric  acid,  the  iron 
must  first  be  separated  by  precipitation  with  ammonium  sulphide,  the  precipi- 
tate washed  with  dilute  ammonium  sulphide,  redissolved  in  hydrochloric  acid, 
boiled,  oxidised  by  potassium  chlorate,  and  then  precipitated  with  ammonium 
hydrate,  as  directed.  In  the  presence  of  manganese  the  solution  should  be 
nearly  neutralised  by  ammonium  hydrate  and  then  boiled  with  excess  of 
ammonium  acetate,  and  the  resulting  ferric  oxy-acetate  collected,  washed, 
dried,  and  ignited  to  Fe2Os. 

17.  ESTIMATION  OF  ALUMINIUM. 

As  Aluminic  Oxide. 

(Practise  upon  i  gramme  of  pure  alum.) 

The  solution  is  precipitated  with  a  slight  excess  of  ammonium  hydrate,  and 
boiled  until  it  only  smells  very  faintly  of  ammonia.  The  precipitated  aluminic 
hydrate  thus  obtained  is  filtered  out,  washed  with  boiling  water,  and  dried. 
The  dry  filter  and  its  contents  are  transferred  to  a  weighed  platinum  crucible, 
and  ignited  to  bright  redness  for  some  time,  allowed  to  cool,  and  weighed 
as  A12O3. 

18.  ESTIMATION  OF  CHROMIUM. 

As  Chromic  Oxide. 

Salts  of  chromium  are  at  once  precipitated  with  ammonium  hydrate,  and  the 
precipitate  washed,  dried,  ignited,  and  weighed  as  Cr^C^.  Soluble  chromates 
are  first  reduced  by  means  of  hydrochloric  and  sulphurous  acids  (or,  instead 
of  the  latter,  spirit  of  wine  may  be  used),  and  the  chromium  precipitated  as 
hydrate  by  ammonium  hydrate,  ignited  and  weighed  as  CrgO^  all  as  described 
above  for  aluminium. 


ESTIMATION  OF  BARIUM,    CALCIUM,   ETC.  149 

19.  ESTIMATION  OF  BARIUM. 

As  Barium  Sulphate. 
(Practise  upon  "5  gramme  of  BaClj  .  2H2O.) 

To  a  solution  in  boiling  water  add  excess  of  sulphuric  acid,  boil  rapidly  foi 
a  few  minutes,  and  set  aside  to  settle. 

The  clear  liquor  is  poured  off  as  closely  as  possible,  and  the  precipitate 
collected  on  a  filter  of  Swedish  paper,  and  washed  with  boiling  water.  The 
filter  and  precipitate  are  next  dried  and  ignited  in  a  weighed  platinum  crucible 
(the  precipitate  being  removed  as  perfectly  as  possible  from  the  paper,  and 
the  latter  first  burned  separately  on  the  crucible  lid,  and  the  ash  added  to  the 
contents  of  the  crucible,  to  avoid  the  reduction  of  BaSO4  to  BaS  by  the  carbon 
of  the  paper).  The  crucible  and  its  contents  having  been  weighed,  and  the 
weight  of  the  crucible  and  filter  ash  deducted,  the  difference  equals  the 
BaSO4. 

20    ESTIMATION  OF  CALCIUM. 
As  Calcium  CarbDnate. 

(Practise  upon  "5  gramme  of  powdered  calc-spar  dissolved  in  dilute  HC1.) 

The  solution  of  the  lime  salt  is  mixed  with  ammonium  chloride,  and  is  then; 
made  alkaline  by  ammonium  hydrate.  Ammonium  oxalate  is  now  added 
in  excess.  The  whole  is  kept  just  below  the  boiling-point  until  the  precipitate 
aggregates,  then  filtered  and  the  precipitate  washed  with  hot  distilled  water 
until  free  from  chlorides.  The  filter  and  contents  having  been  dried  at 
100°  C.,  the  precipitate  is  carefully  transferred  to  a  tared  platinum  crucible 
and  gently  ignited.  It  is  then  moistened  with  a  solution  of  pure  ammonium 
carbonate,  evaporated  to  dryness,  heated  until  no  more  fumes  are  evolved, 
and  then  weighed  as  CaCOs. 

21.  ESTIMATION  OF  MAGNESIUM, 

As  Magnesium  Pyrophosphate. 

(Practise  upon  '5  gramme  of  pure  MgSO4 .  7H2O.) 

The  solution  (which  should  be  strong)  is  mixed  with  some  ammonium 
chloride,  and  then  with  one-third  of  its  bulk  of  ammonium  hydrate,  welt 
cooled,  excess  of  disodium  hydrogen  phosphate  added,  and  the  whole  set 
aside  for  some  hours.  Care  must  be  taken  not  to  touch  the  sides  of  the 
beaker  with  the  stirring  rod,  as  otherwise  particles  of  the  precipitate  will 
adhere  to  them  so  tenaciously  as  to  be  only  removable  with  great  difficulty. 
The  precipitate  is  collected  on  the  filter,  washed  with  a  mixture  of  one  volume 
of  ammonium  hydrate  and  three  volumes  of  water,  till  the  washings  are  free 
from  chlorine,  and  dried.  The  precipitate  is  now  detached  from  the  filter 
and  put  into  a  weighed  platinum  crucible,  the  filter  is  burned  in  the  lid,  the 
ash  added  to  the  contents  of  the  crucible,  and  the  whole  strongly  ignited 
and  weighed  as  Mg2P2O7. 

It  sometimes  happens  that  the  phosphate,  even  after  prolonged  ignition,  is 
very  black.  In  that  case  it  is,  after  cooling,  thoroughly  moistened  with 
nitric  acid,  carefully  dried,  and  re-ignited,  when  it  will  be  found  to  be  perfectly 
white. 

The  B.P.  estimates  magnesium  in  MgSO4  by  simply  precipitating  a  boiling 
solution  with  Na2CO3,  and  collecting,  drying,  igniting,  and  weighing  as  MgO. 


150  GRAVIMETRIC  ANALYSIS  OF  METALS. 

22.  ESTIMATION  OF  POTASSIUM. 

As  Potassium  Platino-Chloride, 
(To  be  practised  upon  "2  gramme  of  pure  KC1.) 

The  solution  is  placed  in  a  small  porcelain  basin,  and  mixed  with  a  good 
excess  of  solution  of  platinic  chloride.  The  whole  is  evaporated  to  dryness 
on  a  water  bath  kept  at  a  temperature  of  about  94°  C.  When  quite  dry  it  is 
again  digested  with  a  few  drops  of  platinic  chloride  solution,  and  taken  up  with 
alcohol.  The  precipitate  is  collected  on  a  weighed  filter,  washed  with  alcohol 
till  the  washings  appear  quite  colourless,  dried  at  100°  C.,  and  weighed  as 
PtCU  •  2KC1. 

23.  ESTIMATION  OF  SODIUM. 

As  Sodium  Sulphate. 
(Practise  upon  '5  gramme  of  pure  NaCl.) 

This  method  is  only  applicable  where  we  have  to  deal  with  a  sodium  salt 
'containing  a  volatile  acid.  The  solution  is  mixed  with  excess  of  sulphuric 
acid  and  evaporated  in  a  weighed  platinum  basin.  When  fumes  of  sulphuric 
acid  become  visible,  the  basin  is  covered  over  with  a  lid  (which  has  been 
weighed  together  with  the  crucible)  and  gradually  heated  till  fumes  cease. 
While  red-hot  the  lid  is  lifted  up  a  little,  and  a  small  lump  of  ammonium 
carbonate  put  in  the  crucible,  which  operation  is  repeated  after  a  few  minutes, 
and  the  residual  NagSO*  is  cooled  and  weighed.  The  object  of  introducing 
the  ammonium  carbonate  is  to  remove  the  last  traces  of  free  sulphuric  acid. 

24.  ESTIMATION   OF  POTASSIUM  AND   SODIUM  IN  PRESENCE  OF 
METALS   OF  FOURTH  GROUP. 

(Practise  upon  the  residue  left  on  evaporating  i  litre  of  ordinary  drinking- 
water,  and  redissolving  in  a  little  dilute  HC1.) 

The  solution  is  first  of  all  precipitated  with  excess  of  barium  chloride, 
which  throws  down  sulphuric,  phosphoric,  etc.,  acids.  Barium  hydrate  (or 
some  milk  of  lime)  is  now  added  in  slight  excess,  when  any  magnesia  will 
also  be  thrown  down.  To  the  filtered  liquid  excess  of  ammonium  carbonate 
is  added,  the  precipitate  is  filtered  out,  and  the  fluid  evaporated  to  dryness  in 
a  platinum  crucible  on  the  water  bath.  When  quite  dry,  it  is  gently  heated 
as  long  as  white  ammoniacal  fumes  are  visible.  The  residue,  which  will  now 
consist  of  alkaline  chlorides,  is,  however,  not  quite  fit  for  weighing,  and  must 
be  purified.  This  is  done  by  redissolving  in  water,  and  adding  a  little 
ammonium  carbonate,  when  a  slight  precipitate  will  form.  After  filtering, 
the  fluid  is  evaporated  (this  time  in  a  tared  platinum  basin)  on  the  water 
bath,  and  when  dry  the  residue  is  gently  heated  to  faint  redness  for  a  minute, 
cooled,  and  weighed.  When  no  sodium  is  present  it  will  now  be  pure 
potassium  chloride  ;  but  should  it  also  contain  sodium  chloride,  it  must  be 
redissolved,  the  potassium  estimated  by  PtCl4,  and  the  sodium  obtained  by 
difference.  This  process  is  one  of  the  most  commonly  occurring  operations, 
because  it  is  required  in  every  full  analysis  of  water,  and  also  of  the  ash  of 
all  vegetable  and  animal  substances,  where  potassium  and  sodium  have  always 
to  be  estimated  in  presence  of  Ca,  Mg,  phosphates,  etc.  It  is  therefore  a 
very  important  one  to  thoroughly  master. 


ESTIMATION  OF  CHLORIDES,   IODIDES,   ETC. 


25.    INDIRECT  ESTIMATION  OF  POTASSIUM  AND  SODIUM. 

The  weighed  mixture  of  KC1  +  Nad  obtained  as  in  24  is  redissolved  in 
distilled  water  and  titrated  with  ^  solution  of  argentic  nitrate  (see  p.  116). 
The  number  of  c.c.  having  been  noted  and  multiplied  by  "003519,  we  obtain 
the  amount  of  Cl  present  in  the  mixed  chlorides.  If  now  all  this  Cl  had 
been  present  as  KC1,  every  35*19  Cl  would  represent  74/02  KC1,  but  if  present 
as  NaCl,  then  35*19  Cl  would  equal  58-07  NaCl,  thus  showing  a  theoretical 
difference  of  15^95,  which  we  will  call  d.  We  therefore  first  calculate  : — 

74*02  x  Cl  found  ...   ..  T^ _, 

=  x  grammes,  if  all  KC1. 

35'I9 

From  this  we  deduct  the  actual  weight  of  the  mixed  chlorides  found,  and 
obtain  a  practical  difference,  which  we  will  call  d'.     Then : — 

d'  x  58-07  _  t|ie  weight  of  NaCl  present  in  the  mixed  chlorides. 
d 

and  by  deducting  this  from  the  total  mixed  chlorides  the  balance  is  KC1. 

26.  ESTIMATION   OF  AMMONIUM. 
As  Ammonium  Platino-Chloride. 

If  the  solution  contains  other  basylous  radicals,  a  known  quantity  of  it  is 
distilled  with  some  slaked  lime  in  a  suitable  apparatus,  and  the  distillate 
received  into  dilute  hydrochloric  acid.  About  three-fourths  is  distilled  over. 
The  distillate  is  then  evaporated  to  dryness  with  excess  of  pure  platinic 
chloride  (free  from  nitre-hydrochloric  acid).  The  dry  residue  is  now  treated 
with  a  mixture  of  two  volumes  of  absolute  alcohol  and  one  of  ether,  collected 
on  a  weighed  filter,  washed  with  the  said  ether  mixture,  dried  at  100°  C., 
and  weighed  as  PtCl4  .  2NH4C1. 

A  less  expensive  method  is  to  distil  the  ammonia  into  a  known  bulk  of 
volumetric  acid,  and  then  check  back  with  volumetric  soda,  so  finding  the 
amount  of  acid  neutralised  by  the  ammonia. 

DIVISION    III.     GRAVIMETRIC   ESTIMATION   OF 

ACID   RADICALS. 

1.  ESTIMATION  OF  CHLORIDES. 

As  Argentic  Chloride. 

(Practise  upon  '5  gramme  pure  NaCl.) 

The  solution  containing  the  chloride  is  precipitated  with  argentic  nitrate. 
Nitric  acid  is  then  added,  and  the  whole  stirred  till  the  liquid  is  perfectly 
clear.  The  precipitate  is  now  treated  as  directed  (see  Silver,  p.  142).  After 
weighing  the  chloride  it  is  calculated  to  Cl. 

2.  ESTIMATION   OF  IODIDES. 

3.  ESTIMATION  OF  BROMIDES. 

4.  ESTIMATION   OF   CYANIDES. 

The  process  for  each  of  these  is  practically  the  same  as  for  chloride.  The 
argentic  cyanide  is,  however,  collected  and  weighed  upon  a  weighed  filter. 
The  argentic  iodide  and  bromide  are  treated  like  the  chloride ;  but  //  a  filter 
is  used,  it  must  be  a  weighed  one.  The  filter  is  afterwards  reweighed,  and 
the  increase  in  weight  is  the  amount  of  argentic  iodide  or  bromide  carried 
on  to  the  filter  during  the  washing  by  decantation. 


1 52  GRA  VI METRIC  ANALYSIS   OF  ACIDS. 

5.  ESTIMATION  OF  AN  IODIDE  IN  THE  PRESENCE  OF  A  CHLORIDE 

AND  A  BROMIDE. 

By  Palladium. 

The  solution,  slightly  acidified,  is  precipitated  with  excess  of  palladious 
chloride.  The  whole  is  then  allowed  to  stand  in  a  warm  place  for  twenty-four 
hours,  so  that  the  precipitate  may  thoroughly  settle.  The  supernatant  liquor 
is  poured  off,  and  the  precipitate  having  been  collected  on  a  filter,  and 
washed,  is  placed  in  a  weighed  platinum  crucible  and  ignited.  The  whole 
is  then  again  weighed,  and  the  weight,  less  that  of  the  crucible  and  filter  ash, 
equals  the  amount  of  metallic  palladium  left  after  ignition,  which  x  2-396  =- 
the  amount  of  iodine  in  the  weight  of  the  sample  taken  for  analysis. 

Note. — A  method  for  estimating  chloride  in  the  presence  of  bromide  will  be  found 
on  page  116. 

6.  ESTIMATION  OF   SULPHIDES. 
By  Conversion  into  Sulphate. 

(Practise  upon  '5  gramme  of  purified  "black  antimony.") 

Fuse  with  a  large  excess  of  a  mixture  of  potassium  nitrate  and  carbonate, 
extract  the  fused  mass  with  water,  filter,  acidulate  with  hydrochloric  acid,  add 
excess  of  barium  chloride,  and  proceed  as  for  a  sulphate  ;  but  calculate  at  the 
last  to  sulphur  instead  of  sulphuric  acid.  Some  sulphides  can  be  attacked 
by  dissolving  in  nitric  acid  with  the  addition  of  successive  small  crystals  of 
potassium  chlorate.  Excess  of  hydrochloric  acid  is  added,  and  the  whole 
having  been  evaporated  to  dryness,  the  residue  is  then  boiled  with  dilute 
hydrochloric  acid,  filtered,  and  the  filtrate  precipitated  with  barium  chloride. 

7.  ESTIMATION   OF   SULPHATES. 

As  Barium  Sulphate. 
(Practise  upon  '5  gramme  of  MgSC>4  •  7H2O.) 

The  solution  is  acidulated  with  hydrochloric  acid,  excess  of  barium  chloride 
is  added,  and  the  whole  boiled.  When  quite  clear  a  little  more  barium 
chloride  is  added,  to  ascertain  whether  all  the  sulphate  has  precipitated.  The 
precipitate  is  now  treated  precisely  as  in  the  barium  estimation  (page  149)  and 
the  resulting  BaSO4  is  calculated  to  sulphate. 

8.  ESTIMATION   OF   NITRATES. 

(A)  In  Alkaline  Nitrates. 

If  nitric  acid  be  required  to  be  estimated  in,  say,  ordinary  nitre,  the  sample 
must  first  be  heated  to  fusion  to  remove  moisture,  and  then  be  quickly 
powdered.  A  weighed  quantity  of  it  is  now  mixed  in  a  platinum  crucible  with 
(exactly)  four  times  its  weight  of  plumbic  sulpha:e.  The  mixture  is  ignited 
till  it  ceases  to  lose  weight,  when  the  loss  will  just  represent  the  amount  of 
nitric  anhydride  in  the  sample  taken  for  analysis. 

The  reaction  is  represented  by  the  following  equation  : — 

PbSO4  +  2KNO3  =  PbO  +  K2SO4  +  2NO2  +  O. 


ESTIMATION  OF  PHOSPHATES.  I53 

(B)  By  Conversion  into  Nitric  Oxide. 
Already  described  at  page  133. 

(C)  By  Conversion  into  Ammonia, 

The  nitrate  is  converted  into  ammonia  by  the  action  of  nascent  hydrogen> 
thus  :— 

HN03  +  4H2  =  NH3  +  3H20. 

The  nascent  hydrogen  may  be  applied  in  various  ways,  as  follows : — 

.1.  By  distillation  with  sodium  hydrate  and  metallic  aluminium,  and 
receiving  the  evolved  ammonia  into  a  known  volume  of  normal 
standard  acid. 

2.  By  acting  on  the  nitrate  for  12  hours  with  zinc  or  iron  and  dilute 
sulphuric  acid,  and  then  adding  excess  of  sodium  hydrate,  and 
distilling  off  the  ammonia  into  a  known  volume  of  normal 
standard  acid. 

The  standard  acid  used  is  then  titrated  by  normal  standard  sodium  hydrate, 
and  the  excess  of  acid  started  with,  over  that  of  alkali  now  used,  gives  the 
number  of  c.c.  of  standard  acid  neutralised  by  the  ammonia.  This  number 
multiplied  by  '06258  =  HNO3  present,  or  by  '05364  =  N2O5- 


9.    ESTIMATION   OF   PHOSPHATES. 

(A)  Estimation  of  the  Strength  of  Free  Phosphoric  Acid. 

i  grm.  of  strong  B.P.  acid  is  evaporated  in  a  weighed  dish  with  2  '5  grms.  of- 
PbO ;  the  dry  residue  is  ignited,  and  should  weigh  2*98  grms.  i  grm.  dilute 
acid  similarly  treated  with  -5  grm.  PbO  should  yield  '6  grm. 

(B)  As  Magnesium  Pyrophosphate  in  Alkaline  Phosphates. 
(Practise  upon  75  gramme  of  pure  Na2HPO4  .  i2H2O.) 

Ammonium  hydrate  and  magnesia  mixture  are  added  in  excess,  and  the 
precipitate  is  treated  as  directed  under  Magnesium  (page  149).  Should  the 
solution  contain  meta-  or  pyro-phosphates  it  must  either  be  previously  boiled 
with  strong  nitric  acid  for  one  hour,  or  be  fused  with  potassium  sodium  car- 
bonate. 

(C)  As  Magnesium  Pyrophosphate  in  the  Presence  of  Calcium  and 

Magnesium. 

(Practise  upon  -5  gramme  of  pure  Ca3(PO4)2  dissolved  in  dilute  HC1.) 

The  solution  (which  must  contain  orthophosphoric  acid,  or,  failing  that, 
should  be  boiled  with  HNO3  as  above)  is  precipitated  with  ammonium  hydrate, 
and  the  precipitate  is  redissolved  m  the  smallest  amount  of  acetic  acid.  The. 
calcium  is  then  removed  by  adding  excess  of  ammonium  oxalate,  and  the 
nitrate  having  been  evaporated  to  a  bulk  not  exceeding  3  ounces  is  cooled, 
treated  with  excess  of  ammonium  hydrate  and  magnesia  mixture,  and  the 
precipitate  is  collected  as  already  described  for  magnesium  (page  149).  This 
process  is  suitable  for  determining  the  "  soluble  phosphates "  in  an  artificial 
manure. 


154  GRAVIMETRIC  ANALYSIS  OF  ACIDS. 

(D)  As  Magnesium  Pyrophosphate  in  the  Presence  of  Iron  and 

Aluminium, 

(Practise  upon  75  gramme  of  B.P.  Ferri phosphas  dissolved  in  dilute  HC1.) 

The  solution  is  mixed  with  excess  of  ammonium  acetate,  boiled,  and  ferric 
chloride  added  till  a  dark-brown  precipitate  forms.  This  is  washed  with 
boiling  water  and  redissolved  in  a  small  quantity  of  dilute  HC1.  About  five 
grammes  (or  more)  of  citric  acid  are  now  introduced,  and  ammonium  hydrate 
is  added  to  the  whole  in  large  excess,  and,  after  cooling,  magnesia  mixture, 
the  precipitate  being  treated  as  for  magnesium.  If  the  addition  of  excess  of 
NH4HO  does  not  produce  a  clear  lemon-yellow  solution,  then  enough  citric 
acid  has  not  been  added. 

(E)  Estimation  as  Phosphomolybdate. 

If  necessary,  the  acid  solution  is  heated  and  precipitated  with  H2S  to 
remove  arsenic.  The  excess  of  B^S  is  boiled  off,  and  large  excess  of  nitric 
acid  is  added.  An  excess  of  ammonium  molybdate  and  ammonium  nitrate 
dissolved  in  nitric  acid  is  now  poured  in,*  the  liquid  boiled,  and  finally  allowed 
to  stand  for  some  hours  in  a  warm  place.  The  precipitate  is  filtered  off,  washed 
with  dilute  alcohol  until  free  from  acidity,  redissolved  in  dilute  ammonium 
hydrate,  the  solution  evaporated  in  a  weighed  dish  on  the  water  bath  and  the 
residue  dried  in  the  water  oven.  Its  weight  -^  28-5  =P2O5  present.  This 
process  is  the  best  for  determining  small  amounts  of  total  phosphates  in  cast 
iron,  waters,  and  soils. 

10.  ESTIMATION  OF  TOTAL  AND  SOLUBLE  PHOSPHATES  IN  AN 
ARTIFICIAL  MANURE  OR  OF  TOTAL  ONLY  IN  SOIL. 

(A)  Total  Phosphates. 

About  2  grammes  of  the  finely  powdered  substance  are  weighed  accurately, 
transferred  to  a  beaker  and  decomposed  with  HC1,  and  where  necessary  with 
the  addition  of  a  drop  or  two  of  HNOs.  The  solution  is  then  evaporated  to 
dryness  in  a  water  bath,  taken  up  with  HC1,  and  after  digestion  the  insoluble 
silicious  matter  is  separated  by  filtration  ;  a  weighed  quantity  of  citric  acid  is 
added,  the  solution  heated  up  nearly  to  boiling  point,  and  a  weighed  quantity 
of  ammonium  oxalate  added.  The  quantities  used  must  vary  with  the 
substance  under  examination,  the  knowledge  only  being  acquired  by 
experience  ;  but  it  is  seldom  necessary  to  add  more  than  2  grammes  citric  acid 
or  2:5  grammes  ammonium  oxalate.  The  free  acid  is  then  just  neutralised 
with  dilute  ammonia,  and  acetic  acid  added,  to  decidedly  acid  reaction.  The 
liquid  is  kept  simmering  for  a  few  minutes  with  constant  stirring,  and  after 
standing  a  short  time  the  calcium  oxalate  is  filtered  out.  Great  care  must 
be  observed  not  to  have  too  large  an  excess  of  ammonium  oxalate  present,  as 
magnesium  oxalate  in  an  ammoniacal  solution  is  somewhat  easily  precipitated. 
To  the  filtrate  ammonia  of  '880  sp.  gr.  is  added  to  about  one-fourth  of  the 
bulk ;  and  to  the  liquid,  which  must  remain  clear,  or  only  slowly  throw  down 
a  small  precipitate,  due  to  the  magnesia  present,  magnesia  mixture  is  added 
in  moderate  excess.  The  liquid  must  be  set  aside,  with  occasional  stirring 
for  the  precipitate  to  form — the  time  required  being  principally  determined 
by  the  quantity  of  alumina  present.  It  is  best,  however,  to  allow  it  to  stand 
over  night,  although  in  cases  where  the  alumina  is  absent,  or  small,  the  prc- 

*  This  solution  is  prepared  by  dissolving  10  grammes  of  molybdic  acid  in  417  c.c.  of 
ammonia  solution  (-96  sp.  gr.),  and  then  adding  to  125  c.c.  of  nitric  acid,  sp.  gr.  r2O. 


ESTIMATION  OF  ARSENIATES  AND   CARBONATES.       15^ 

cipitation  will  be  found  to  be  complete  in  two  hours.  The  precipitate  is  then 
separated  from  the  liquid  by  filtration,  dissolved  in  as  little  HC1  as  possible, 
and  reprecipitated  with  one-third  of  its  bulk  of  ammonia.  After  allowing  to 
stand  for  two  hours  with  occasional  stirring,  it  may  be  filtered,  and  after 
drying  converted,  by  ignition  in  a  weighed  platinum  crucible,  into  Mg2P2O7, 
and  weighed  as  such. 

The  calcium  oxalate  is  converted  into  CaCO3  by  gentle  ignition,  weighed, 
dissolved  in  HC1,  and  tested  for  P2O5,  which  may  be  present  in  small 
quantities,  and  if  so  it  should  be  determined. 

The  Mg2P2O7  is  calculated  to  Ca3(PO4)2  unless  a  full  analysis  is  being 
made,  when  it  is  calculated  to  P2O5,  and  divided  pro  rata  among  the  bases 
actually  found  to  be  in  combination  with  it. 

Note. — Recent  researches  have  sho\vn  that  by  the  addition  of  a  sufficiently  large  amount 
of  citric  acid,  all  the  intermediate  steps  of  the  process  are  saved,  it  being  only  necessary 
to  afterwards  add  the  _excess  of  ammonia  and  magnesia  mixture.  By  this  method,  a 
large  excess  of  citric  acid  having  been  first  introduced,  ammonia  is  added,  and  should  no 
precipitate  occur,  it  is  followed  by  the  magnesia  mixture  ;  but  if  even  a  cloud  should  appear, 
more  citric  acid  must  go  in,  until  sufficient  has  been  added  to  cause  a  perfectly  clear  solution 
on  the  subsequent  addition  of  ammonia.  The  whole  must  stand  in  the  cold  for  at  least 
twenty-four  hours  before  filtering  off  the  precipitate  of  ammonium  magnesium  phosphate,  so 
that,  after  all,  no  time  is  saved  by  the  new  method,  but  the  risk  of  loss  is  less,  because  the 
intermediate  filtration  (to  remove  calcium)  is  avoided. 

(B]  Soluble  Phosphates. 

Five  grammes  of  the  manure  are  well  triturated  in  a  mortar  with  distilled 
water,  washed  into  a  stoppered  250  c.c.  flask,  and  made  up  to  the  mark  with 
water.  After  standing  with  occasional  shaking  for  two  hours,  100  c.c.  (  =  2 
grammes  of  sample)  is  drawn  off  by  a  pipette  into  a  beaker,  2  grammes  of 
citric  acid  and  2^5  grammes  of  ammonium  oxalate  are  dissolved  in  the  liquid, 
which  is  then  treated  with  ammonia,  acetic  acid,  etc.,  as  above  described.  If 
the  amount  of  soluble  calcium  comes  out  low,  the  process  should  be  repeated, 
using  such  a  weighed  quantity  of  ammonium  oxalate  as  will  just  remove  it 
from  solution.  This  is  because  the  great  source  of  error  in  phosphate 
estimations  is  the  use  of  excess  of  oxalate,  causing  the  precipitation  of 
magnesium  oxalate  with  the  magnesium  ammonium  phosphate.  The 
adoption  of  the  direct  citric  acid  and  ammonia  method  (given  above)  of 
course  avoids  any  difficulty  in  this  respect.  The  Mg2P2O7  is  calculated  to 
Ca3(PO4)2,  and  reported  as  "  phosphate  made  soluble." 

11.  ESTIMATION  OF  ARSENIATES. 

Arseniates  are  estimated  precisely  like  phosphates  ;  but  the  precipitate 
of  ammonium  magnesium  arseniate  is  dried  at  105°  C.  on  a  weighed 
filter,  as  already  directed  under  Arsenic.  The  precipitate  thus  dried  is 
(MgNH4AsO4)2 .  H2O;  or,  for  simplicity  of  calculation,  MgNH4AsC>4  .  |H2O. 

12.  ESTIMATION  OF  CARBONATES. 

A  carbonate  is  estimated  by  the  loss  of  weight  it  undergoes  by  the  dis- 
placement of  its  carbonic  anhydride  by  an  acid.  A  small  and  light  flask  is 
procured  and  fitted  with  a  cork  through  which  passes  a  tube  (c)  containing 
fragments  of  calcium  chloride  (see  fig.  35).  A  weighed  quantity  of  the 
carbonate  is  introduced  into  the  flask  with  a  little  water,  and  a  small  test-tube 
about  two  inches  long  is  filled  with  sulphuric  acid  and  dropped  into  the  flask, 
so  that,  being  supported  in  an  upright  position,  none  of  the  acid  shall  mix 
with  the  carbonate.  The  cork  is  put  in,  and  the  weight  of  the  whole 


,56  GRA  VI METRIC  ANALYSIS  OF  ACIDS. 

apparatus  having  been  carefully  noted,  it  is  inclined  so  as  to  allow  the  acid 
to  run  from  the  small  tube  into  the  body  of  the 
flask.  Effervescence  sets  in,  the  carbonate  is  dis- 
solved, and  the  COs,  escaping  through  the  calcium 
chloride  tube,  is  deprived  of  any  moisture  it  might 
carry  with  it.  When  all  action  has  ceased,  and 
the  whole  has  cooled,  air  is  drawn  through  the 
apparatus  to  displace  the  remaining  CO2  and 
it  is  once  more  weighed.  The  difference  between 
the  two  weights  gives  the  amount  of  CO2  evolved. 
A  better  apparatus  is  that  figured  (No.  36),  in  which  c  is  the 

flask,  A  the  tube  to  contain  HC1  to  decompose  the  carbonate,       Fig.  36 

and  B  a  tube  containing   strong    H2SO4,  through  which   the    evolved  CO^ 

must  pass,  and  so  be  perfectly  deprived  of  moisture. 

13.  ESTIMATION  OF  BORIC  ACID  IN  EQUATES. 

This  is  best  done  by  distilling  off  the  boron  in  the  form  of  methyl  borate, 
and  finally  estimating  it  as  calcium  borate.  The  apparatus  required  is  a 
distilling  flask  heated  by  a  water-bath  and  fitted  with  a  tap-funnel,  the  tube 
of  which  reaches  nearly  to  the  bottom  of  the  flask.  The  side  delivery-tube 
is  attached  to  an  upright  condenser  having  a  spiral  worm  and  ending  in  a 
receiver  standing  in  a  dish  of  cold  water  and  furnished  with  a  set  of  bulbs 
containing  dilute  ammonia,  to  ensure  against  the  escape  of  any  methyl  borate. 

The  weighed  quantity  of  the  boric  acid  (or  borate)  is  put  into  the  flask 
with  as  little  liquid  as  possible,  and  i  c.c.  of  nitric  acid  having  been  added, 
the  whole  is  distilled  to  dryness.  10  c.c.  of  methyl  alcohol  are  then 
introduced  by  the  funnel  and  entirely  distilled  off,  which  operation  is  repeated 
four  times.  2  c.c.  of  an  equal  mixture  of  nitric  acid  and  water  are  again 
added,  distilled  off,  and  the  treatment  with  methyl  alcohol  is  continued  until 
a  drop  of  the  distillate,  absorbed  into  filter-paper,  ceases  to  burn  with  a  green 
flame.  While  this  distillation  is  proceeding,  some  pure  lime  (10  grammes  for 
every  '5  gramme  of  borate  taken)  is  put  into  a  platinum  dish,  heated  for  some 
time  over  the  blow-pipe,  cooled  under  the  desiccator  and  weighed.  The 
weighed  dish  and  lime  having  been  placed  on  ice,  the  contents  of  the 
receiver  and  bulbs  are  added  to  it  and,  after  standing  for  twenty  minutes, 
the  whole  is  very  cautiously  evaporated  at  a  temperature  below  59°  C.  The 
heat  is  then  gradually  increased  until  the  mass  is  quite  dry  and  the  whole  is 
finally  ignited  over  the  blow-pipe  and  weighed.  The  increase  in  weight  is 
the  B2O3  from  the  weight  of  sample  started  with. 

14.  ESTIMATION  OF  OXALIC  ACID. 

As  Calcium  Carbonate. 

The  solution  is  made  alkaline  with  ammonium  hydrate  and  precipitated 
with  calcium  chloride.  The  precipitate  is  washed  till  free  from  chlorides, 
dried,  ignited,  and  finally  weighed  as  carbonate,  as  directed  under  Calcium 
(page  149). 

15.  ESTIMATION  OF  TARTARIC  ACID. 
As  Calcium  Oxide. 

The  solution  (which  must  contain  no  other  bases  than  K,  Na,  or  NH4)  is 
made  faintly  alkaline  by  sodium  hydrate,  and  precipitated  by  excess  of  calcic 
chloride.  The  precipitate  is  washed  with  cold  water,  dried,  ignited  (with  the 
blowpipe),  and  weighed  as  calcic  oxide. 


FULL  MINERAL  ANALYSIS  OF  POTABLE    WATER.        157 

16.  ESTIMATION  OF  SILICIC  ACID. 

(A)  In  Soluble  Silicates. 

By  soluble  silicates  are  meant  those  which  are  either  soluble  in  water  of 
in  hydrochloric  acid.  The  solution  (which  must  contain  some  free  HC1)  is 
evaporated  to  dryness  on  the  water  bath,  and  the  residue  dried  for  an  hour 
at  120°  C.  (248°  F.).  After  cooling,  the  mass  is  moistened  with  strong  hydro- 
chloric acid,  and  then  boiled  with  water,  thus  leaving  an  insoluble  residue  of 
pure  silica — SiO2 — which  is  collected  on  a  filter,  washed,  dried,  ignited,  and 
weighed. 

(J3)  In  Insoluble  Silicates. 

These  bodies  must  be  decomposed  by  mixing  a  weighed  quantity  of  the 
finely  powdered  substance  with  four  times  its  weight  of  sodium  potassium 
carbonate,  and  fusing  the  whole  for  about  half  an  hour.  ( When  alkalies  have 
to  be  estimated,  a  separate  special  fusion  must  be  made  with  barium  hydrate,  or 
pure  lime  mixed  with  ammonium  chloride,  instead  of  the  double  carbonate.}  The 
crucible  must  be  well  covered  during  fusion.  After  cooling,  the  residue  is 
treated  with  dilute  and  warm  HC1  until  effervescence  ceases,  evaporated  to 
dryness,  and  treated  as  above  described  at  120°  C.  (248°  F.),  etc. 

DIVISION    IV.      GRAVIMETRIC   SEPARATIONS. 

This  department  is  beyond  the  scope  of  the  present  edition.  When  the  student  has  practised 
all  the  contents  of  the  book  up  to  this  point,  he  will  already  have  a  sufficiently  general  idea  of 
chemical  analysis  to  enable  him  to  fix  the  line  of  work  he  desires  to  make  his  speciality.  If 
this  be  mineral  analysis,  he  must  pass  to  a  larger  book,  such  as  "  Fresenius,"  to  complete  his 
knowledge.  So  as  to  give,  however,  some  idea  of  how  the  preceding  processes  may  be  joined 
in  performing  the  full  analysis  of  a  mixture,  we  take  the  following  example,  because  it  is  a 
standard  one,  and  give  a  sketch  of  the  manner  of  working  in  performing  : — 

The  Full  Analysis  of  the  Mineral  Contents  of  a  Sample  of  Ordinary 
Potable  Water. 

Step  I.  Take  the  total  solid  residue  of  100  c  c.  (calculated  in  grains  per  gallon)  as  directed 
in  Chapter  X.,  to  serve  as  a  check  on  the  results ;  then  ignite  and  again  weigh  :  loss  =  organic 
and  volatile  matter. 

Step  II.  Evaporate  2000  c.c.  of  the  water  to  dryness  in  a  large  porcelain  dish.  Moisten 
the  residue  with  10  c.c.  of  distilled  water,  and  then  add  200  c.c.  of  dilute  alcohol  '92  sp.  gr. : 
having  gently  detached  it  all  from  the  dish,  filter  and  wash  with  similarly  diluted  alcohol  till 
practically  nothing  more  dissolves.  This  procedure  is  useful  because  it  separates  the  salts 
present  thus  : — 

(a)  The  filtrate  may  contain  all  salts  of  K  and  Na,  chlorides  and  nitrates  of  Ca  and  Mg,  and 
the  sulphate  of  Mg. 

(b]  The  insoluble  residue  may  contain  the  sulphate  and  carbonate  of  Ca  and  the  carbonate 
of  Mg,  together  with  any  iron  and  silicious  matter  present. 

(l)  Analysis  of  the  filtrate. 

(a)  Evaporate  till  the  spirit  is  driven  off,  cool,  transfer  to  a  200  c.c.  flask,  and  make  up  to 
the  mark  with  distilled  water.  Divide  into  two  portions  of  loo  c.c.  respectively,  marking 
them  A  and  B. 

(6)  To  A  add  NH4C1,  NH4HO  and  (NHJ2C,O4,  to  precipitate  the  Ca,  and  estimate  ai 
usual  as  CaCO3.  Calculate  to  CaO,  and  then  x  2  =  CaO  present  as  Cl  or  NO,,  in  the 
original  2000  c.c.  of  water  taken. 

(c)  To  filtrate  and  washings  from  (3),  concentrated  to  50  c.c.  and  cooled,  add  Na2HPO4, 
to  precipitate   Mg,  treat  as  usual,  and  weigh  as  Mg2P2O7.      Calculate  to  MgO,  and  then 
X  2  =  MgO  present  as  Cl,  SO4,  or  NO3  in  the  original  2000  c.c.  of  water. 

(d]  To  B  acidulate  with  HC1  and  add  BaCl2  to  precipitate  sulphate.     Treat  as  usual  and 
weigh  as  BaSO4.     Calculate  to  SO,,  and  then  X  2  =  total  SOS  present  in  the  original  2000 
E.C.  of  water  taken  in  combination  with  K  or  Na. 


I58  GRAVIMETRIC   SEPARATIONS. 

(e)  The  filtrate  and  washings  from  (,/)  are  evaporated  to  a  low  bulk  rendered  alkaline  with 
pureCa(HO)2,  the  separation  for  alkalies  given  at  page  150  gone  through,  and  the  K  and  Na 
present  both  estimated  as  chlorides.     Results  X  2  =  total  K  and  Na  present  in  the  2000  c.c. 
of  water  started  with. 

(f)  The  residue  from  (e)  is  dissolved  in  a  little  water,  and  the  K  estimated  thereon  by 
PtCl4  in  the  usual  manner  and  calculated  to  K2O  (see  page  150).     An  equivalent  amount  of 
KC1  (calculated  from  this  ICO)  is  then  deducted  from  residue  (e),  and  the  balance  is  NaCl, 
which  is  calculated  to  Na2O. 

(2)  Analysis  of  the  insoluble  portion. 

(a)  This  is  washed  from  the  filter  with  distilled  water  and  then  boiled  with  100  c.c.  of  II .AD 
and  HC1  added  till  effervescence  ceases.  Any  insoluble  is  filtered  out,  washed  with  boiling 
H,O,  dried,  ignited,  and  weighed  =  silicious  matter  in  the  2000  c.c.  of  water  started  with. 

(3)  The  filtrate  and  washings  are  warmed  with  a  drop  or  two  of  HNO3  and  mixed  with 
NH4C1  +  NH4HO,  and  the  iron  estimated  if  present  as  Fe2O3,  and  result  calculated    to 
Fe  =  total  Fe  in  the  2000  c.c.  of  water  taken. 

(c)  Divide  filtrate  and  washings  into  two  equal  parts,  A  and  B. 

(d)  The  portion  A  is  precipitated  with  (NH4)aCaO4,  and  the  calcium  estimated  as  CaCO3 
and  calculated  to  CaO.     Result  X  2  =  total  CaO  as  carbonate  or  sulphate  in  the  original 
2000  c.c.  of  water  taken. 

(<?)  The  filtrate  from  (</)  is  concentrated  to  a  low  bulk,  cooled,  and  Na2HPO4  added  with 
excess  of  NH4HO,  and  the  Mg  estimated  as  usual  as  Mg2P2O7>  and. calculated  to  MgO. 
Result  X  2  =  total  MgO  present  as  carbonate  in  the  original  2000  c.c.  of  water. 

(/")  The  portion  K  is  acidulated  with  HC1,  and  the  sulphate  estimated  by  BaCl2,  weighed 
as  BaSO4,  and  calculated  to  SO3.  Result  X  2  =  total  SO3  in  combination  with  Ca  in  the 
original  2000  c.c.  of  water. 

Step  III.  Evaporate  250  c.c.  of  the  water  to  a  bulk  of  2  c.c.,  and  treat  in  the  nitrometer  to 
estimate  the  nitric  acid  (see  page  134)-  Resulting  NO  calculated  to  N2O5  and  x  8  =  total 
N,O5  present  in  2000  c.c.  of  water. 

Step  IV.  Take  the  amount  of  chlorides  volumetrically  (page  116)  in  100  c.c.  of  the  water. 
Result  X  20  =  Cl  in  2000  c.c.  of  water. 

Step  V.     Calculation  of  results. 

(a)  All  our  results  being  in  grammes  or  fractions  of  the  same  from  2000  c.c.  of  water,  each 
must  be  multiplied  by  35,  which  will  bring  them  all  to  grains  per  imperial  gallon  (parts  in 
70,000).  The  analysis  is  then  stated  as  follows  (example  taken  from  actual  practice)  : — 

A  sample  of  water  yielding  20 -I  grains  of  total  solids  per  gallon,  of  which  '45  grain  was 
"  organic  and  volatile  matter,"  and  the  balance  (19*65  grains)  was-mineral  matter,  showed  on 
analysis  : — 


)  In  the  portion  soluble  in  spirit  : 

grains  per  gallon. 

Potassium  oxide      .         .         .     '2704 
Sodium  oxide  .        .  1*4097 

Chlorine          .         .  .1-2133 

Sulphuric  anhydride  .     '6803 

Calcium  oxide  .        .    none. 

Magnesium  oxide   .  .     none. 

Nitric  anhydride     .         .         .     none. 


(b)  In  the  portion  insoluble  in  spirit : 

grains  per  gallon. 

Calcium  oxide       .  .         .     7'3953 

Magnesium  oxide  .  .     I  'oooo 

Sulphuric  anhydride  .     17647 

Silicious  matter     .  '2000 

Ferric  oxide .  '0500 

Total  found  .  13-9837 


From  this  residue  is  now  to  be  always  deducted  an  amount  of  oxygen  equivalent  to 
the  chlorine  found,  because  all  the  bases  have  been  calculated  to  oxides,  while  haloid  salts 
contain  no  oxygen.  The  chlorine  found  is  1-2133,  and  — 

—    =  *2737  °xvgen»  equivalent  to  Cl  found. 

Performing  the  deduction,  we  have — 

I3'9^37  —  '2737  ==  137100  grains  of  solid  matter  actually  found. 

The  total  residue,  after  driving  off  organic  matter,  was  19  '65  grains  per  gallon,  and   the 
difference  is  due  to  CO;,  unestimated,  thus  : — 

"19-65  —  13-71  =  5-94  grains  of  CO.,  per  gallon. 
Adding  now  this  CO2  to  the  substances  actually  estimated,  we  get — 

Total  substances  found  +  CO2  =  19  65, 

Actual  residue  found  =  19^65, 
which  proves  our  analysis  to  be  correct. 

It  now  remains  to  calculate  how  these  bases  and  acids  are  probably  combined  as  salts 
actually  present,  by  the  following  general  rules  of  affinity,  thus  :  — 

(a)  In  the  portion  soluble  in  spirit.  (l)  Any  sulphuric  anhydride  will  prefer  the  bases  in 
the  following  order :  K,  Na,  Mg.  (2)  Chlorine  will  prefer  the  bases  in  the  same  order 
after  the  SO3  is  satisfied.  Therefore  we  first  calculate  our  K2O  to  K2SO4,  which  gives  -50  and 
uses  up  '2296  of  our  SO3,  and  the  balance  of  SO3  ( '4507)  we  calculate  to  Na.,SO4  This  gives 
•80  Na^SO^  and  leaves  1*0604  NajO  not  as  sulphate  and  therefore  existing  as  chloride. 


FULL  MINERAL  ANALYSIS  OF  POTABLE    WATER.        159 

Calculating  accordingly,  we  get  2-oo  of  NaCl,  which  just  uses  up  all  our  chlorine.     There- 

fore this  portion  contained  altogether  — 

Potassium  sulphate         .....  -50 

Sodium  sulphate    ......  -80 

Sodium  chloride    ......         2-oo 

(£)  /;/  the  portion  insoluble  in  spirit,     (i)  The  SO3  found  will  all  be  present  as  CaSO4, 

and  the  balance  of  CaO  and  all  the  MgO  will  be  as  carbonates.      Therefore  17647  SO3 

calculated  to  CaSO4  becomes  3-00  and  uses  up  1-2353  °f  ^aO»  leaving  6*16  to  be  calculated 

to  CaCO3.     This  yields  iroo  CaCO3,  and  the  roo  of  MgO  found,  calculated  to  MgCO, 

gives  2-10.     Thus  this  portion  contains  —  • 

Calcium  sulphate  ......         3-00 

Calcium  carbonate          .....       iroo 

Magnesium  carbonate    .....         2gio 

Putting  now  the  whole  analysis  together,  we  have  — 

Potassium  sulphate        ....  -50 

Sodium  sulphate   .         .  .  -80 

Sodium  chloride    ......         2-oo 

Calcium  sulphate  ...  .         .         3-00 

Calcium  carbonate  ,         «  iroo 

Magnesium  carbonate    .  2  10 

Ferric  oxide  .  .  -05 

Silica    .....  -20 

Organic  and  volatile  matter  ....  -45 


Total  residue    20'  IO 


CHAPTER    IX. 


ULTIMATE    ORGANIC  ANALYSIS. 

THIS  process  consists  in  estimating  the  amount  of  each  element  present  in 
any  organic  compound,  as  distinguished  from  proximate  analysis,  which 
estimates  the  amounts  of  the  compounds  themselves. 

I.    LIST   OF   APPARATUS   REQUIRED. 

1.  A  combustion  furnace,  which  is  a  series  of  Bunsen  burners  arranged  in  a  frame 

so  as  to  gradually  raise  a  tube  placed  over  them  to  a  red  heat.  The  tube  lies 
in  a  bed  made  of  a  series  of  firebricks,  which  confine  the  heat  and  make  it 
play  all  round  the  tube  (see  fig.  37). 

2.  Combustion  tubes  made  of  hard  glass,  not  softening  at  a  red  heat.     These  tubes 

are  closed  at  one  end  by  drawing  out  before  the  blowpipe  and  turning  up. 
The  mode  of  doing  this  is  illustrated  in  fig.  38. 


Fig.  39- 


Fig.  37. 


01 

ft 

c 

d 

^-- 

Fig.  38. 

Fig.  40. 


3.  U  tubes  packed  with  perfectly  dry  calcium  chloride  in  small  fragments,  so  as  to 

allow  the  free  passage  of  gases  (illustrated  in  fig.  39),  and  hereafter  referred 
to  for  brevity  as  "  CaCL  tubes." 

4.  Bulbs  charged  with  strong  solution  of  potassium  hydrate  (i  in  i),  hereafter  for 

brevity  referred  to  as  '•  KHO  bulbs."  Two  common  forms  of  such  bulbs  are 
illustrated  in  fig.  40. 

5.  Bulbs  for  absorbing  ammonia  and    intended   to  be  charged  with  dilute  acid  of 

known  strength,  and  hereafter  referred  to  as  "nitrogen  bulbs"  for  brevity. 
Two  common  forms  of  such  bulbs  are  illustrated  in  fig.  41. 

6.  Graduated  tubes  closed  at  one  end,  to  hold  50  c.c.,  and  graduated  from  the  closed 

end  downwards  in  ^  of  a  c.c.,  used  for  collecting  gases  and  measuring 
them  after  collection,  hereafter  referrred  to  as  "gas-collecting  tubes"  for 
brevity  (fig.  42). 

7-  A  deep  cylindrical  vessel  of  glass  filled  with  water  and  furnished  with  a  thermo- 
meter dipping  in  the  water ;  the  whole  sufficiently  deep  to  permit  of  the 
entire  immersion  of  the  gas-measuring  tubes,  and  wide  enough  at  the  top  to 
admit  the  hand,  as  shown  in  fig.  43.  This  is  hereafter  called  the  "  measuring 
trough  "  for  brevity. 

160 


ESTIMATION  OF  CARBON  AND  HYDROGEN. 


161 


3  Glass  towers,  filled  in  one  limb  with  fragments  of  CaCl2  to  absorb  moisture,  and 
in  the  other  with  fragments  of  soda-lime  to  absorb  carbon  dioxide.  These  are 
illustrated  in  fig.  44,  and  are  used  for  freeing  any  air  which  may  be  caused  to 
pass  through  them  from  moisture  and  CO3;  hereafter  called  "air-purifying 
towers  "  for  brevity. 

II.     ESTIMATION   OF   CARBON   AND   HYDROGEN. 

I.  Liebig's  Process. — This  process  is  performed  by  heating  a  weighed 
quantity  of  the  substance  in  a  tube  with  some  body  readily  parting  with 
oxygen  at  a  red  heat,  such  as  cupric  oxide  or  plumbic  chromate,  by  which 
the  hydrogen  and  carbon  of  the  organic  body  are  respectively  oxidised  into 
water  and  carbonic  anhydride.  These  products  are  passed  first  through  a 
weighed  tube  containing  calcium  chloride,  which  retains  the  water,  and  then 
through  a  weighed  bulb  apparatus  containing  potassium  hydrate,  which  absorbs 
the  carbonic  anhydride.  After  the  experiment  is  finished,  the  increase  in 
weight  of  the  tubes  is  calculated  thus : 

As  H..O  :  H2  :  :  increase  in  CaCl2  tube  :  x. 

As  CO.,  :  C  :  :  increase  in  KHO  bulbs  :  x. 


Fig.  41. 


Fig.  43- 


Fig.  43- 


Fig.  44. 


The  details  of  the  actual  process  are  as  follows  : — 
(i)  Preliminary  steps. 

(a)  Choose  a  combustion  tube,  drawn  out  and  sealed  at  one  end  (fig.  38),  about 
eighteen  inches  long  and  \  to  f  inch  in  bore,  and  fit  two  corks  to  it,  one 
whole  and  the  other  bored  so  as  to  be  all  ready  to  take  the  bulb  end  of  the 
CaCl2  tube  (fig.  39),  which  must  fit  air-tight  when  pushed  through  the  cork. 

(£)  Measure  out  sufficient  CuO  (powdered)  to  fill  the  combustion  tube,  and  put  it 
into  a  small  pear-shaped  hard  glass  flask  over  a  good  il  Bunsen  "  to  heat  to  dull 
redness  and  drive  off  all  moisture.  Then  remove  the  source  of  heat,  cork 
it  up,  and  let  it  cool. 

(f)  While  the  CuO  is  cooling  weigh  your  CaCL  tube  and  your  KIIO  bulbs 
(fig.  40),  and,  having  noted  their  respective  weights,  close  the  open  ends  by 
means  of  short  pieces  of  black  rubber  tubing,  having  bits  of  glass  rod  put  in 
to  act  as  stoppers. 

(of)  '4  gramme  of  KC1O3  is  then  to  be  weighed  out,  powdered  and  heated  gently 
in  a  porcelain  capsule  until  it  just  fuses.  The  fused  mass  is  crushed  to 
powder  by  a  glass  rod  and  the  capsule  put  under  the  desiccator. 

(0  '3  to  '4  gramme  of  the  substance  is  (if  solid)  weighed  on  a  watch  glass  and 
put  Binder  the  desiccator.  If  liquid,  a  very  minute  stoppered  tube  (to  be 
obtained  at  any  apparatus  shop)  is  weighed,  and  having  been  filled  with  the 
liquid  it  is  closed  and  again  weighed,  the  difference  being  the  weight  of 
liquid  taken. 

(/)  Sufficient  asbestos  fibre  to  make  a  plug  that  will  occupy  about  \  inch  of  the 
combustion  tube  is  heated  to  redness  and  cooled  under  the  desiccator. 

(,;,')  A  long  wire  with  a  curled  end  is  got  ready* 

II 


1 62  ULTIMATE  ORGANIC  ANALYSIS. 

(2)  Charging  the  combustion  tube.     When  the   CuO  has  cooled  suf- 

ficiently so  that  it  can  be  handled,  the  KClOs  is  first  dropped 
into  the  combustion  tube  and  is  followed  by  four  inches  of 
CuO  (rapidly  transferred  from  the  flask  with  as  little  exposure 
to  the  air  as  possible).  The  weighed  substance,  if  solid,  is 
then  dropped  in,  and  immediately  followed  by  another  three 
inches  of  CuO.  The  long  wire  is  then  used  to  mix  the  sub- 
stance through  the  upper  six  inches  of  CuO,  taking  care  not 
to  disturb  the  lower  inch  or  the  KC1O3  (if  a  liquid  only  two 
inches  of  CuO  are  put  in,  and  then  the  bottle  is  dropped  in, 
and  followed  by  five  inches  cf  CuO).  The  tube  is  now  filled 
with  CuO  to  within  two  and  a  half  inches  of  its  end ;  the 
asbestos  is  introduced  so  as  to  form  a  loose  plug,  leaving  a 
space  of  an  inch  between  it  and  the  charge,  and  the  tube  is 
securely  corked.  It  is  then  laid  flat  upon  the  table  and  tapped 
thereon  until  its  contents  settle  down,  so  leaving  a  clear  passage 
for  any  gases  along  the  upper  part  of  the  tube,  which  is  then 
placed  in  the  furnace  (fig.  37)  with  the  corked  end  just  pro- 
truding. The  cork  is  removed  and  the  CaCl2  tube  is  attached 
by  means  of  the  perforated  cork  (taking  care  to  put  the 
"bulbed"  limb  next  the  tube),  and  to  the  other  end  of  that 
the  KHO  bulbs  are  attached  by  means  of  a  piece  of  black 
rubber  tubing,  seeing  that  the  larger  side  of  the  bulbs  is  next 
the  CaCls  tube.  The  whole  apparatus  is  now  complete,  and 
after  testing  it  for  air  tightness  of  the  cork  and  joints  (by  gently 
warming  the  inner  side  of  the  KHO  bulbs  so  as  to  expel  some 
of  the  air,  and  seeing  that  on  cooling  the, liquid  stands  at  a 
higher  level  in  the  inner  bulb  than  before),  we  are  ready  to 
perform  : — 

(3)  The  Combustion.     We  first  light  the  first  six  burners  next  the  bulbs, 

and  when  the  front  part  of  the  tube  is  red-hot  we  carefully 
light  the  other  burners  one  at  a  time,  so  as  to  cause  the  heat  to 
travel  gradually  backwards.  The  art  is  to  so  regulate  our  heat 
as  never  to  produce  bubbles  of  gas  passing  through  the  bulbs 
at  a  more  rapid  rate  than  can  be  distinctly  counted.  When 
the  whole  tube  is  red-hot,  all  except  the  last  inch,  and  the 
evolution  of  gas  has  practically  ceased,  we  light  the  last  burner 
and  cause  an  evolution  of  oxygen  from  the  KC1O3  which  clears 
the  tube  of  any  residual  gases  and  carries  them  through  the 
bulbs.  The  gas  is  then  turned  off,  and  when  cooled  the  CaGl* 
tube  and  KHO  bulbs  are  detached  and  reweighed,  and  the 
increase  noted  in  each  case. 

(4)  Calculation  of  results.     The  following  is  an  example  of  the  method 

of  calculating ;  the  substance  under  analysis  being  sugar- 
candy. 

Weight  of  sugar  taken      .....  '475  gramme. 

Potash  bulbs  after  combustion  weighed    .        .        .     79-113  grammes, 
„     before        ,,  „  7^3§2 

Difference,  due  to  CO2    .         .         .         731         ,, 

Calcium  chloride  tube  after  combustion  weighed      .     23*605  grammes. 
„  before         ,,  „  .     23-330 

Difference,  due  to  1IVO  .         .         .         '275         ,„ 


ESTIMATION  OF  CARBON  AND  HYDROGEN.  163 


(C)  12  x  7^1  (H,)  2  X  '271; 

<pssi r  =  ''"4  cw  .8  = 

Total  sugar  taken     .         .         .         .         .         •         •     '475 
Total  C  and  II  found -22996 

Difference,  due  to  oxygen         .         .     '24504 

Or,  in  percentage — Carbon       .         .         .         .         .         .         .41-98 

Hydrogen 6-43 

Oxygen 51-59 

10Q-QO 

Special  Notes  to  the  Foregoing  Process. 

(a)  Substances  containing  sulphur,  phosphorus,  arsenic,  chlorine,  or  any  halogen, 
are  best  mixed  with  fused  and  powdered  plumbic  chromate  instead  of  cupric 
oxide,  so  as  to  avoid  the  formation  of  volatile  cupric  compounds. 

(^)  When  the  substance  also  contains  nitrogen,  the  front  part  of  the  combustion- 
tube  must  be  plugged  with  a  roll  of  bright  copper  gauze  about  four  inches 
long  instead  of  the  asbestos.  This  is  to  reduce  any  oxide  of  nitrogen,  which 
if  allowed  to  pass  into  the  potash  would  be  absorbed  and  count  as  carbon 
dioxide.  The  copper,  however,  takes  the  oxygen,  and  only  leaves  nitrogen, 
which  passes  unabsorbed. 

(-;)  Very  refractory  bodies,  such  as  coal,  starch,  etc.,  are  best  burned  with  plumbic 
chromate,  or  should  be  done  by  the  improved  process,  in  a  current  of  air  or 
of  oxygen,  to  be  next  considered. 

II.  The  Improved  Modern  Process.— The  difficulty  of  Liebig's  method  lies 
in  the  hygroscopic  nature  of  CuO,  which  is  so  marked  that  it  is  scarcely 
possible  to  transfer  it  from  the  drying  flask  to  the  tube  without  getting  some 
moisture,  thus,  of  course,  vitiating  the  hydrogen  determination,  to  avoid  which 
we  proceed  as  follows  : — 

A  combustion  tube,  about  twenty  inches  long  and  open  at  each  end,  is 
charged  as  shown. 


*  9"         &'    $'  c  jf  * 

Fig.  44A.— a  is  the  front  end,  to  which  the  CaQ2  tube  and  KHO  bulbs  are  attached  ;  a'  is  the  back  ena, 
to  which  a  set  of  "air-purifying  towers"  (rig.  44)  are  attached;  c  is  a  layer  tot  granulated  CuO,. 
twelve  inches  long  ;  g  and  g'  are  small  rolls  of  copper  gauze,  ahout  half  an  inch  long,  to  keep  the 
CuO  in  its  place  ;  6  is  a  platinum  boat  to  contain  the  weighed  substance,  either  soiid  or  in  a  little 
tube  as  already  described  ;  g"  is  a  roll  of  oxidised  copper  gauze,  three  and  a  half  inches  long. 

If  the  body  also  contains  nitrogen,  the  roll  g  must  be  made  of  bright 
copper  gauze,  four  inches  long,  thus  nearly  filling  the  empty  space  shown. 
To'  perform  the  process  the  tube  is  placed  in  the  furnace,  and  a'  having, 
been  connected  to  the  "  towers,"  they  are  in  turn  attached  to  a  gasometer 
containing  air  or  oxygen.  The  roll  g'  and  the  boat  b  having  been  withdrawn 
the  layer  of  CuO  is  heated  to  redness,  and  a  slow,  steady  stream  of  air  or 
oxygen  is  passed  from  the  gasometer.  When  the  CuO  is  quite  dry  the  air  is- 
stopped,  the  heat  is  reduced,  the  weighed  tube  and  bulbs  are  attached  to  a, 
and  the  cork  a'  having  been  opened,  the  boat  and  roll  are  replaced,  and  the 
whole  again  closed  up,  and  the  air  gently  turned  on.  The  CuO  having  again 
been  raised  to  a  redness,  the  burner  under  the  boat  is  lighted,  and  the  heat 
cautiously  applied,  so  as  to  gradually  burn  the  substance  entirely  away.  At 
the  end  of  the  process  the  air  is  stopped,  and  the  CaClo  tube  and  KHO  bulbs, 
detached  and  weighed.  Any  number  of  combustions  can  be  done  one  after 
another  by  simply  re-oxidising  the  reduced  CuO,  by  heating  and  turning  or* 
the  air  for  a  few  minutes,  and  then  proceeding  again  as  before.  This  is  the 
really  practical  method,  and  many  analysts  prefer  to  suck  the  air  through,  by- 
means  of  an  aspirator  attached  to  the  outer  end  of  the  KHO  bulbs,  instead' 
of  driving  it  from  a  gasometer.  In  using  oxygen  it  is,  however,  always  driven 
from  one  of  the  steel  tubes  in  which  it  is  sold  in  the  compressed  state. 


Xft4  ULTIMATE  ORGANIC  ANALYSIS. 

III.  ESTIMATION  OF  NITROGEN. 

The  estimation  of  nitrogen  in  all  compounds,  not  being  nitrites  or  nitrates, 
is  conducted  as  follows  : — 

I.  The  Method  of  Varrentrapp  Modified, — This  depends  for  its  success 
on  the  fact  that  when  nitrogenous  substances  are  strongly  heated  with  sodium 
hydrate  they  are  decomposed,  forming  a  carbonate  and  oxide  with  the  oxygen 
from  the  hydroxyl,  and  liberating  hydrogen,  which  then  combines  with  the 
nitrogen  to  form  ammonia.  So  as  to  prevent  fusion  of  the  glass  tubes  em- 
ployed, solution  of  sodium  hydrate  is  evaporated  to  dryness  with  calcium 
oxide,  and  the  resulting  mixture,  known  as  soda-lime,  is  heated  to  redness  and 
preserved  for  use. 

(1)  Preliminary  steps  : — 

(a)  Choose  a  combustion  tube,  about  fifteen  inches  long  and  a 
half-inch  bore,  drawn  and  sealed  as  in  fig.  38,  and  fitted  with  a 
perforated  cork  to  take  the  bulbs. 

(^)  Measure  out  enough  soda-lime  to  fill  the  tube  and  put  it  over 
the  gas  to  get  dry  in  a  small  basin  and  then  cool  under  the 
desiccator.  (If  the  soda-lime  is  already  fresh  and  dry  this  is 
unnecessary,  and  we  then  only  measure  it  out  and  put  the 
quantity  we  want  into  a  little  dry  stoppered  bottle;  but  the 
quantity  must  always  be  measured,  otherwise  mistakes  occur  in 
filling  the  tube.) 

(c)  Put  a  glass  mortar  and  a  funnel  with  its  limb  cut  off  close  to 

the  neck  on  the  top  of  the  oven  to  warm. 

(d)  Put  a   little  asbestos   on   to   ignite,  and  then  cool   under    the 

desiccator. 

(e)  Measure  20  c.c.  of  equivalent  seminormal  volumetric  acid  from 

a  burette  into  a  beaker.  Take  the  "nitrogen  bulbs''  (fig.  41), 
and  by  sucking  at  the  wide  end  with  the  narrow  point  immersed 
in  the  acid,  transfer  as  much  of  it  as  possible  to  the  bulbs  with- 
out loss,  and  then  cover  the  beaker  up  and  set  it  aside. 
(/)  Weigh  out  '4  to  2  grammes  of  the  substance  according  to  its 
richness  in  nitrogen. 

(2)  Charging  the  tube.     This  should  be  done  over  a  sheet  of  glazed 

paper,  so  that  anything  spilt  can  be  easily  picked  up  without 
loss,  and  the  short-ended  funnel  should  be  used  to  assist  in 
filling  the  tube.  About  an  inch  of  our  soda-lime  is  first  put 
in,  then  half  of  it  is  pounded  up  in  the  mortar  with  the 
weighed  substance  and  transferred  to  the  tube.  The  mortar 
is  then  rinsed  with  some  more  soda-lime,  and  these  rinsings 
having  been  poured  into  the  tube  it  is  filled  up  with  soda-lime 
to  within  two  and  a  half  inches  of  the  end.  A  plug  of  asbestos 
is  then  put  in,  so  as  to  leave  about  one  inch  free  space  between 
it  and  the  charge,  and  the  tube  is  laid  on  the  table  and  tapped 
to  cause  a  channel  for  gases  at  the  top,  as  already  described 
above. 

(3)  Combustion.     The  tube  is  placed  in  the  furnace,  and  the  bulbs 

having  been  attached  by  the  perforated  cork  the  first  four 
burners  are  lighted.  When  the  front  is  red-hot,  the  heat  is 
gradually  passed  back  as  already  described,  carefully  regulating 
•The  evolution  of  gases.  When  all  the  tube  is  red-hot  and 
gases  cease  to  pass,  a  piece  of  black  rubber  tube  is  slipped 
over  the  exit  of  the  bulbs,  and,  suction  being  applied  to  it,  the 
drawn-out  end  at  the  back  of  the  combustion  tube  is  broken 


ESTIMATION  OF  NITROGEN.  165 

with  a  pair  of  tongs.  A  current  of  air  is  thus  caused  to  pass 
through  and  to  sweep  all  residual  gases  into  the  bulbs.  The 
gas  is  then  put  out,  and  when  cool  the  bulbs  are  detached  and 
we  then  proceed  to — 

(4)  The  titration.  The  contents  of  the  bulbs  having  been  rinsed 
back  into  the  same  beaker  as  originally  contained  the  acid 
(set  aside  for  this  purpose),  taking  care  to  wash  the  bulbs 
well  and  add  the  washings  to  the  beaker,  litmus  is  added, 
and  the  whole  is  titrated  with  seminormal  soda,  made  to 
exactly  balance  the  acid,  and,  the  number  of  c.c.  used  having 
b^en  deducted  from  20,  the  difference  is  the  c.c.  of  acid 
neutralised  by  the  ammonia  given  off  during  combustion. 
Now  i  litre  of  equivalent  normal  acid  (B.P.  strength)  would 
neutralise  16*94  grammes  of  NH?  =  13 '9 4  grammes  of  N  ;  e.g. 
each  c.c.  would  =  '01394  N  for  norrKril  acid,  '00697  for  semi- 
normal  acid,  or  '003485  for  quadrinormal ;  therefore,  multiply 
the  number  of  c.c.  of  acid  neutralised  by  one  of  these  factors 
according  to  the  strength  of  acid  employed,  and  the  answer 
gives  weight  of  N  in  the  weight  of  substance  taken,  which  is 
then  calculated  to  percentage. 

II.  Origins!  Method  of  Varrentrapp.— This  was  conducted  in  the  same 
way,  only  the  bulbs  were  charged  with  dilute  HC1,  and  at  the  end  of  the 
combustion  their  contents  were  precipitated  with  PtCl4  and  the  resulting  pre- 
cipitate of  PtCl4  (NH4C1)2  collected  on  a  tared  filter,  dried  at  100°  C.,  weighed 
and  calculated  to  N2. 

III.  The  Process  of  Dumas. — This  consists  in  measuring  the  amount  of  pure 
nitrogen  evolved,  and  is  suitable  for  certain  organic  bases  and  for  compounds 
containing  nitrosyl  (NO)  or  nitryl  (NOg),  in  which  the  soda-lime  fails  to  con- 
vert all  the  nitrogen  into  ammonia. 

The  combustion  tube  (which  in  this  case  is  twenty-six  to  twenty-eight  inches 
long)  is  packed  (i)  with  six  inches  of  dry  sodium  hydrogen  carbonate;  (2) 
with  a  little  pure  cupric  oxide ;  (3)  with  the  weighed  substance  mixed  with 
CuO  ;  (4)  with  more  pure  CuO  ;  and  lastly  with  a  considerable  length  of  pure 
spongy  metallic  copper ;  and  the  whole  is  closed  by  a  good  cork,  through  which 
passes  a  bent  delivery  tube,  dipping  under  the  surface  of  mercury  in  a  small 
pneumatic  trough.  Heat  is  first  applied  to  the  very  end  portion  of  the 
NaHCO3,  until  sufficient  COs  has  been  given  off  to  entirely  drive  all  the  air 
out  of  the  apparatus,  which  is  ascertained  by  collecting  a  little  of  the  gas 
passing  off  and  seeing  that  it  is  entirely  absorbed  by  solution  of  potassium 
hydrate.  A  graduated  gas-collecting  tube  (fig.  42)  is  then  filled,  one-third 
with  strong  solution  of  KHO,  and  the  remainder  with  mercury,  and  carefully 
inverted  into  the  mercury  trough  so  that  no  air  is  admitted,  and  placed  over 
the  mouth  of  the  delivery  tube.  Combustion  is  now  commenced  at  the  front 
of  the  tube  and  gradually  carried  backwards  as  usual.  The  gases  evolved  are 
COo  and  N,  the  former  of  which  is  absorbed  by  the  KHO  and  the  latter 
collects  in  the  graduated  tube.  When  the  heat  reaches  the  back,  the  remainder 
of  the  NaHCO3  is  decomposed,  and  the  carbonic  anhydride  given  off  chases 
any  trace  of  nitrogen  out  of  the  tube.  The  collecting  tube  is  then  closed  by 
a  small  cup  containing  mercury,  and  transferred  to  the  measuring  trough 
(fig.  43),  and  entirely  immersed  therein.  After  leaving  it  until  its  contents 
have  acquired  the  temperature  of  the  water,  it  is  raised  so  that  the  level  of 
the  water  inside  and  outside  the  tube  is  equal,  and  the  volume  is  read  off. 
The  temperature  and  pressure  being  noted,  the  weight  of  the  nitrogen  is, 
obtained  by  the  species  of  calculation  already  described  at  page  133. 


166  ULTIMATE  ORGANIC  ANALYSIS. 

IV.  Kjeldahl's  Process. — This  method  is  rapidly  superseding  combustion. 
It  depends  upon  the  fact  that  when  most  nitrogenous  bodies  are  heated  with 
excess  of  strong  sulphuric  acid  their  nitrogen  is  converted  into  ammonium 
sulphate,  from  which  latter  the  ammonia  may  be  liberated  by  excess  of  alkali, 
•distilled  off  and  titrated.  No  special  apparatus  is  really  required  other  than 
a  hard  glass  flask  and  the  usual  distilling  arrangements ;  but  where  rapidity, 
combined  with  accuracy,  is  desired,  the  following  special  arrangements 
should  be  provided. 

(1)  Hard  glass  long-necked  flasks,  purchaseable  as  "Kjeldahl's  flasks." 

(2)  A  stand  to  hold  the  flasks  in  an  inclined  position  over  Bunsen  burners. 

(3)  A  distilling  arrangement  constructed  as  follows  :  A  copper  flask,  capable  of  holding 
500  c.c..  is  fi  ted  with  a  rubber  cork,  through  which  passes  the  bottom  end  of  a 
"  Soxhlet"  tube.     The  other  end  of  this  tube  is  closed  by  a  rubber  cork,  pierced 
by  two  holes  ;  through  one  of  these  passes  the  stem  of  a  tapped  funnel,  and  through 
the  other  the  end  of  a  block-tin  tube,  f  inch  in  diameter,  which  is  carried  up  to  an 
altitude  of  18  inches,  and  then  brought  down  again,  its  other  end  passing  through 
a  rubber  cork  into  a  tapered  glass  connector,  dipping  to  the  bottom  of  a  receiving 
flask,  which  latter   is  placed  in  a  vessel   of  cold  water.      In  this  apparatus  the 
"Soxhlet  "  acts  as  an  ami-spurting  appliance,  and  the  use  of  a  metal  flask  enables 
very  rapid  distillation  to  be  performed.     The  receiving  flask  should  be  marked 
at  300  c.c.,  and  should  have  a  total  capacity  of  about  400  c.c. 

From  0-2  to  2*0  grms.  of  substance  is  taken  (according  to  its  richness 
in  nitrogen),  and  is  placed  in  a  Kjeldahl  flask,  with  20  c.c.  of  strong  sulphuric 
acid  (free  from  nitrous  compounds),  and  75  gramme  of  red  mercuric  oxide. 
The  flask  is  placed  on  the  stand  and  heated  up  to  nearly  the  boiling-point  of 
the  acid  for  ten  minutes.  If  the  liquid  should  tend  to  become  clear,  no 
further  addition  is  needed;  but  if  it  be  still  black,  5  to  10  grammes  of 
potassium  sulphate  are  added  and  the  heating  continued.  When  the  liquid 
has  become  clear  and  colourless,  or  nearly  so,  the  flask  is  allowed  to  cool, 
200  c.c.  water  is  added,  and  the  whole  poured  into  the  funnel  of  the  distilling 
apparatus.  A  further  quantity  of  about  200  c.c.  of  water  is  used  to  rinse 
out  the  flask,  and  is  also  poured  into  the  funnel,  followed  by  75  c.c.  of  50 
per  cent,  sodium  hydrate  solution  and  20  c.c.  of  a  4  per  cent,  solution  of 
potassium  sulphide.  The  soda  is  to  neutralise  the  sulphuric  acid,  and  the 
potassium  sulphide  to  prevent  the  formation  of  mercur-ammonium  com- 
pounds. The  stop-cock  of  the  funnel  is  closed,  and  50  c.c.  of  decinormal 
sulphuric  acid  having  been  placed  in  the  receiving  flask,  the  distillation  is 
proceeded  with.  When  the  liquid  in  the  receiver  has  risen  to  the  mark  the 
distillation  is  stopped,  and  its  contents  are  titrated  with  decinormal  alkali, 
using  methyl-orange  indicator.  The  number  of  c.c.  of  alkali  used  is  deducted 
from  50,  and  the  balance  multiplied  by  -001394  =  nitrogen  in  the  weight  of 
substance  started  with.  This  nitrogen  x  6*33  =  the  proteids  present. 

IV.  ESTIMATION   OF    CHLORINE, 

Chlorine  is  estimated  by  combustion  of  the  substance  in  a  tube  filled  with 
pure  calcium  oxide,  when  the  chlorine  displaces  oxygen  and  turns  part  of  the 
oxide  into  calcium  chloride.  After  combustion  the  contents  of  the  tube  are 
dissolved  in  diluted  nitric  acid,  filtered,  and  the  Cl  precipitated  by  argentic 
nitrate.  (See  Gravimetric  Estimation  of  Chlorine,  p.  151.) 

V.  ESTIMATION   OF   SULPHUR   AND   PHOSPHORUS. 

Sulphur  and  phosphorus  are  estimated  by  fusing  about  2  grammes  of  the 
solid  substance  in  a  silver  crucible,  with  24  grammes  of  pure  potassium 
hydrate  and  3  grammes  of  pure  potassium  nitrate.  After  fusion  the  sulphur 
and  phosphorus  (which  have  been  converted  into  sulphates  and  phosphates 
respectively)  are  estimated  by  dissolving  the  residue  in  water,  slightly  acidu- 
lating with  hydrochloric  acid,  and  precipitating  as  usual.  (See  Gravimetric 
Estimation  of  Sulphates  and  Phosphates,  p.  152.) 


CHAPTER    X. 

THE    ANALYSIS    OF    WATER,    AIR,    AND    FOOD. 


DIVISION   I.     THE    SANITARY    ANALYSIS    OF    WATER. 

IN  the  present  state  of  our  knowledge  it  is  an  open  question  whether  a 
chemical  analysis  alone  will  under  any  circumstances  enable  a  definite  opinion 
to  be  formed  as  to  the  safety  of  any  water  supply  unless  supplemented  by  a 
bacteriological  investigation.  The  latter,  however,  being  evidently  out  of  the 
province  of  this  work,  the  chemical  points  are  now  given  quantum  valeant. 

1.   Collection  of  the  Sample. 

This  is  to  be  taken  in  a  clean,  stoppered  "  Winchester  quart  "  bottle, 
previously  entirely  filled  with  the  water,  and  emptied  before  finally  filling  up 
and  introducing  the  stopper.  The  sample  should  be  kept  in  a  dark  place, 
and  analysed  with  as  little  delay  as  possible. 

2.  Colour. 

This  is  to  be  judged  by  looking  at  a  column  of  water  in  a  colourless  glass 
tube  2  feet  long,  and  held  over  white  paper.  The  presence  of  a  greenish- 
yellow  colour  is  an  adverse  indication. 

3.  Odour. 

An  8-ounce  wide-mouthed  stoppered  bottle,  free  from  odour,  is  half  filled 
with  the  water,  warmed  in  the  water  bath  to  38°  C,  shaken,  and  then  the 
stopper  is  removed  and  the  odour  instantly  noted.  Peaty  waters,  and  those 
containing  marked  amounts  of  sewage,  can  frequently  be  thus  detected  by 
a  practised  nose. 

4.   Suspended  Solids. 

Pass  a  litre  of  the  turbid  water  through  a  dried  and  tared  filter.  Dry  the 
filter  and  deposit  at  120°  C.  and  weigh.  The  gain  in  weight  of  the  filter 
is  the  weight  of  suspended  matter  in  a  litre  of  water. 

5.   Total  Solid  Residue. 

Heat  a  platinum  basin  of  about  130  c.c.  capacity  to  redness,  cool  it  under 
the  desiccator,  and  weigh.  Introduce  100  c.c.  of  the  water,  and  evaporate 
over  a  low  gas  flame  until  reduced  to  about  10  c.c. ;  then  place  it  on  the 
water  bath  till  dry.  Finally,  heat  it  in  the  air  bath  at  105°  C.  until  it 
ceases  t,o  lose  weight,  cool  under  the  desiccator,  and  weigh.  Having  deducted 

167 


168         .THE  ANALYSIS  OF  WATER,   AIR,   AND  FOOD. 

the  tare  of  the  basin,  the  difference  in  milligrammes  x   10  =  total  residue  in 
parts  per  million,  or  the  same  x   7-4-  10  =  grains  per  gallon.     Example  : — 

Weight  dish  +  resickie     .         .         .     89-336 
Tare  of  dish 89-300 

•036  ox-  36  milligrammes  ; 
36  x  7 

then =  25*2  grains  per  gallon. 

10 

The  residue  should  now  be  gradually  heated  to  redness,  and  the  presence 
of  organic  matter  carefully  looked  for  as  indicated  by  charring;  also  the 
nature  of  the  same,  by  whether  the  odour  on  burning  is  purely  carbonaceous 
(like  burning  sugar)  or  nitrogenous  (like  burning  hair).  This  latter  is  an 
especially  unfavourable  indication. 

6,   Chlorine. 

Solutions  required : 

(a)  4-789  grammes  pure  crystallised  argentic  nitrate,  dissolved  in  1000  c.c.  of  dis- 
tilled water.  Each  c.c.  of  this  solution  =  'OOI  (one  milligramme]  of  chlorine. 

(l>)  5  grammes  potassium  chromate  dissolved  in  100  c.c.  distilled  water,  and  a  weak 
solution  of  argentic  nitrate  dropped  in  until  a  slight  permanent  red  precipitate 
is  produced,  which  is  allowed  to  settle  in  the  bottle. 

Process. — Put  100  c.c.  of  the  water  into  a  white  basin,  add  a  few  drops  of 
the  chromate  solution,  and  titrate  with  the  silver  solution  from  a  burette, 
graduated  in  ~  of  c.c.,  until  a  faint  permanent  change  of  colour  is  produced, 
as  already  described  (Chap.  VII.,  p.  115).  Note  the  number  of  c.c.  used, 
multiply  by  10,  and  the  result  will  be  chlorine  in  parts  per  million,  or  multiply 
by  7  and  divide  by  10,  which  will  give  grains  per  gallon.  The  water  itself 
must  be  perfectly  neutral ;  if  acid  it  must  be  first  shaken  with  a  little  pure 
precipitated  chalk.  The  presence  of  a  large  amount  of  chlorine  with 
excessive  ammonia  and  albuminoid  ammonia  indicates  that  the  organic 
impurity  is,  probably,  of  animal  origin. 

7.  Nitrogen  as  Nitrates. 

(a)  Crum  Process. — 250  c.c.  of  the  water  are  evaporated  to  a  small  bulk, 
the  chlorine  precipitated  with  saturated  solution  of  argentic  sulphate,  filtered, 
and  the  filtrate  concentrated  in  a  basin  to  2  c.c.  A  nitrometer  (see  p.  133) 
is  charged  with  mercury,  and  the  three-way  stopcock  closed,  both  to  measuring 
tube  and  waste-pipe.  The  concentrated  filtrate  is  poured  into  the  cup  at  the 
top  of  the  measuring  tube,  and  the  vessel  which  contained  it  rinsed  with  i  c.c. 
of  water,  and  the  contents  added.  The  stopcock  is  opened  to  the  measuring 
tube,  and,  by  lowering  the  pressure  tube,  the  liquid  is  sucked  out  of  the  cup 
into  the  tube.  The  basin  is  again  rinsed  with  5  c.c.  of  pure  strong  sulphuric 
acid,  and  this  is  also  transferred  to  the  cup  and  sucked  into  the  measuring 
tube.  The  stopcock  is  once  more  closed,  and  12  c.c.  more  sulphuric  acid 
put  into  the  cup,  and  the  stopcock  opened  to  the  measuring  tube  until  10  c.c. 
of  acid  have  passed  in.  The  excess  of  acid  is  discharged,  and  the  cup  and 
waste-pipe  rinsed  with  water.  Any  gas  which  has  collected  in  the  measuring 
tube  is  expelled  by  opening  the  stopcock  and  raising  the  pressure  tube,  taking 
care  no  liquid  escapes.  The  stopcock  is  closed,  the  measuring  tube  taken  from 
its  clamp  and  shaken  by  bringing  it  slowly  to  a  nearly  horizontal  position  and 
then  suddenly  raising  it  to  a  vertical  one.  This  shaking  is  continued  until  no 
more  gas  is  given  off,  the  operation  being  complete  in  fifteen  minutes.  Now 


THE  SANITARY  ANALYSIS   OF   WATER.  169. 

prepare  a  mixture  of  one  part  of  water  with  five  parts  of  sulphuric  acid,  and  let 
it  stand  to  cool.  After  an  hour,  pour  enough  of  this  mixture  into  the  pressure 
tube  to  equal  the  length  of  the  column  of  acidulated  water  in  the  working  tube, 
bring  the  two  tubes  side  by  side,  raise  or  lower  the  pressure  tube  until  the 
mercury  is  at  the  same  level  in  both  tubes,  and  read  off  the  volume  of  the 
nitric  oxide.  This  volume,  expressed  in  c.cs.  and  corrected  to  normal  tem- 
perature and  pressure,  gives,  when  multiplied  by  '175,  the  nitrogen  in  nitrates, 
in  grains  per  gallon,  if  250  c.c.  of  the  water  have  been  used.  According  to 
some  authorities  the  precipitation  of  the  chlorides  is  not  necessary. 

(b)  Copper-Zinc  Process. — This  must  be  carried  out  as  follows  : — A  wet 
copper-zinc  couple  is  prepared  by  taking  a  piece  of  clean  zinc  foil,  about  3  in. 
by  2  in.,  and  immersing  it  in  a  solution  of  copper  sulphate,  containing  about 
3  per  cent,  of  the  pure  crystallised  salt.  A  copious  and  firmly  adherent 
coating  of  black  copper  is  speedily  deposited  upon  the  surface  of  the  zinc,, 
which  must  be  allowed  to  remain  in  the  solution  until  the  deposit  is  thick 
enough,  but  not  for  too  long  a  time,  or  it  will  become  pulverulent  and 
not  adhere  firmly  to  the  zinc — three  or  four  minutes  will  generally  be 
sufficient. 

The  zinc  coated  with  copper  must  then  be  removed  from  the  solution  and 
the  couple  thoroughly  washed,  first  with  distilled  water,  and  finally  with  the 
water  to  be  analysed,  in  order  that  this  may  replace  the  adhering  distilled 
water.  It  is  then  put  into  a  clean  6-  or  8-ounce  wide-mouthed  stoppered  glass 
bottle,  and  covered  with  100  c.c.  of  the  water  to  be  analysed.  If  the  water  be 
very  soft  a  small  addition,  say  one  part  per  1000,  of  sodium  chloride  will 
accelerate  the  reaction.  The  stopper  must  then  be  inserted  in  the  bottle  and 
the  water  allowed  to  remain  overnight  in  a  warm  place.  If  still  greater  speed 
be  necessary  the  temperature  may  be  raised  to  90°  or  100°  F.  (32°  or  38°  C.). 
With  hard  water  it  is  preferable  to  add  a  small  quantity  of  pure  oxalic  acid,  to 
precipitate  the  lime  and  quicken  the  reaction.  When  the  reduction  is  complete 
the  fluid  contents  of  the  bottle  are  to  be  transferred  to  a  retort  with  200  c.c. 
of  ammonia-free  distilled  water,  and,  the  retort  having  been  attached  to  a 
condenser,  the  contents  are  distilled  till  the  distillate  which  comes  over  gives 
no  colour  with  "  Nessler."  The  distillate  is  then  "  Nesslerised,"  as  already 
described  (Chap.  VII.,  page  136),  and  the  number  of  milligrammes  of  NHa: 
found  are  calculated  to  N  (x  14-7-17),  and  then  the  resulting  milligrammes, 
of  N  x  7-7-  10  =  grains  per  gallon,  or  x  10  only  =  parts  per  million. 


8.   Nitrites. 

Solutions  required : — 

1.  Dilute  sulphuric  acid  (i  of  acid  to  2  of  water). 

2.  5  grammes  of  metaphenylenediamine,  and  sufficient  sulphuric  acid  to  form  an  acid' 

reaction  dissolved  in  1000  c.c.  of  water. 

3.  O'^oC  grammes   of  pure   dry   silver  nitrite  dissolved   in   hot  water,  adding  pure 

sodium  chloride  so  long  as  a  precipitate  is  formed,  diluting  to  1000  c.c.  with 
water,  and  setting  aside  to  deposit  its  silver  chloride.  100  c.c.  of  the  clear 
liquid  are  then  diluted  to  I  litre.  I  c.c.  of  this  solution  contains  "OI  milli- 
gramme NoO3. 

Process. — Put  100  c.c.  of  the  water  in  a  glass  cylinder,  and  add  i  c.c.  each 
of  solutions  i  and  2.  Prepare  three  other  cylinders  by  diluting  5  c.c.,  i  c.c.,, 
and  2  c.c.  respectively,  to  100  c.c.  with  pure  water,  and  adding  i  c.c.  each  of 
solutions  i  and  2.  Compare  the  shade  of  the  water  cylinder  with  that  of  the 
others,  as  described  under  "  Nesslerising."  The  amount  of  N2Os  in  the  water 
is  equal  to  that  of  the  comparison  cylinder  having  the  same  shade. 


170  THE  ANALYSIS  OF   WATER,   AIR,   AND  FOOD. 

9.   Ammonia  and  Albuminoid  Ammonia. 

These  two  indications  are  successively  taken  on  the  same  quantity  of  water. 
The  former  is  an  estimation  of  the  ammonia  present  in  the  water  in  the  form 
of  ammonium  salts  or  similar  compounds  readily  decomposed  by  a  weak 
alkali,  while  the  latter  shows  the  ammonia  derived  from  the  decomposition  of 
nitrogenous  organic  matter  under  the  joint  influence  of  an  oxidising  agent 
(KaMr^Og)  and  a  hydrating  agent  (KHO),  and  is  therefore  a  measure  of  the 
nitrogenous,  and  consequently  presumably  dangerous,  organic  matters  con- 
tained in  the  water  under  examination. 

The  solutions  and  apparatus  required  are  : — 

(a)  Sodium  carbonate. 

A  2O-per-cent.  solution  of  recently  ignited  pure  sodium  carbonate. 

(l>)  Alkaline  potassium  permanganate  solution. 

Dissolve  200  parts  of  potassium  hydrate  and  8  parts  of  pure  potassium  per- 
manganate in  I2OO  parts  of  distilled  water,  and  boil  the  solution  rapidly  till 
concentrated  to  1000  parts,  cool,  and  keep  in  a  well-stoppered  bottle. 

(c)  Distilled  water  "which  is  f fee  from  ammonia. 

Distilled  water  which  gives  no  reaction  with  Nessler  test  is  pure  enough.  But,  if 
this  is  not  available,  take  the  purest  distilled  water  procurable,  add  p«re  ignited 
sodium  carbonate  in  the  proportion  of  I  part  per  1000,  and  boil  briskly  until 
at  least  one-fourth  has  been  evaporated. 

(d)  A  4O-ounce  stoppered  retort,  with  a  neck  small  enough  to  pass  loosely  into  the 

internal  tube  of  a  Liebig's  condenser  to  the  extent  of  6  inches  (see  illustration, 
Chap.  I.,  page  4).  The  joint  between  the  retort  and  condenser  is  made  by 
an  ordinary  india-rubber  ring— such  as  those  used  for  the  tops  of  umbrellas — 
which  has  been  previously  soaked  in  a  dilute  solution  of  soda  or  potash,  being 
stretched  over  the  retort  tube  in  such  a  position  that  when  the  retort  tube  is 
inserted  in  the  condenser  it  shall  fit  fairly  tightly  within  the  mouth  of  the  tube 
about  half  an  inch  from  the  end. 

(f)  All  the  materials  for  "  Nesslerising"  (see  Chap.  VII.,  page  136). 
The  process  is  as  follows  : — 

(a)  For  ammonia. — First  test  a  little  of  the  waiter  with  tincture  of 
cochineal,  to  see  if  it  shows  an  alkaline  reaction.  Put  500  c.c.  of  distilled 
water  into  the  retort,  and  distil  until  50  c.c.  of  the  distillate  gives  no  colour 
with  ik  c.c.  of  Nessler,  thus  rendering  the  whole  apparatus  "  ammonia-free." 
Let  the  whole  cool,  pour  out  the  distilled  water  (which  may  be  saved  for 
.ammonia-free  water),  put  in  500  c.c.  of  the  water  to  be  analysed,  and,  if  it  has 
not  an  alkaline  reaction,  make  it  alkaline  with  a  drop  or  two  of  the  sodium  car- 
bonate solution.  The  distillation  should  then  be  commenced,  and  not  less 
than  100  c.c.  distilled  over.  The  receiver  should  fit  closely,  but  not  air-tight, 
into  the  condenser.  The  distillation  should  be  conducted  as  rapidly  as  is 
compatible  with  a  certainty  that  no  spurting  takes  place.  After  100  c.c.  have 
been  distilled  over,  the  receiver  should  be  changed,  that  containing  the  distil- 
late being  stoppered  to  preserve  it  from  access  of  ammoniacal  fumes.  100  c.c. 
measuring-flasks  make  convenient  receivers.  The  distillation  must  be  con- 
tinued until  50  c.c.  more  are  distilled  over ;  and  this  second  portion  of  the 
distillate  must  be  tested  with  Nessler's  re-agent  to  ascertain  if  it  contains  any 
ammonia.  If  it  does  not,  the  distillation  for  free  ammonia  may  be  discon- 
tinued, and  this  last  distillate  rejected  ;  but,  if  it  does  contain  any,  the  distilla- 
tion must  be  continued  still  longer,  until  a  portion  of  50  c.c.,  when  collected, 
shows  no  coloration  with  the  Nessler  test.  The  whole  of  the  distillates 
must  be  mixed  together  and  "  Nesslerised  "  in  the  usual  manner,  and  the  total 
number  of  milligrammes  of  ammonia  found  are  multiplied  by  2,  which  gives 
milligrammes  per  litre  (parts  per  million).  This  number  in  turn  multiplied 
by  7  and  divided  by  100  gives  grains  per  gallon  of  ammonia. 


THE  SANITARY  ANALYSIS   OF   WATER.  171 

(b)  For  albuminoid  ammonia. — As  soon  as  the  distillation  above  referred  to 
has  been  started,  50  c.c.  of  the  alkaline  potassium  permanganate  solution  are 
placed  in  a  basin  with  150  c.c.  of  distilled  water,  and  boiled  gently  during  the 
whole  time  that  the  free  ammonia  is  distilling,  adding  some  ammonia-free 
water  if  necessary,  to  prevent  too  much  concentration.  [The  object  of  this  is' 
to  ensure  the  entire  evolution  of  any  trace  of  ammonia  present  in  the  alkaline 
permanganate,  thus  avoiding  a  check  analysis,  as  usually  recommended.]  At 
the  same  time  a  few  fragments  of  clay  tobacco-pipe  are  put  into  a  platinum 
dish,  heated  to  redness,  and  then  kept  warm  till  required  for  use.  When  the 
distillation  of  the  ammonia  is  complete,  take  out  the  stopper  of  the  retort  and 
pour  in  the  boiled  alkaline  permanganate  by  means  of  a  perfectly  clean  funnel 
with  a  long  limb  ;  then  remove  the  funnel  and  drop  in  the  fragments  of  clay 
pipe.  Now  replace  the  stopper  and  continue  the  distillation,  when  the 
albuminoid  ammonia  will  begin  to  come  over.  After  200  c.c.  have  been 
distilled,  change  the  receiver  and  take  off  50  c.c.  at  a  time,  as  already  described, 
until  the  last  50  comes  over  ammonia-free.  Mix  the  distillates,  "  Nesslerise  " 
-and  calculate  as  for  the  ammonia,  noting  the  total  result  as  albuminoid 
ammonia  in  parts  per  million  or  grains  per  gallon.  Great  care  must  be  taken 
that  no  ammonia  is  kept  in  the  room  devoted  to  water  analysis,  and  that  all 
/receivers  used  are  first  insured  to  be  perfectly  ammonia-free  by  proper  rinsing 
with  ammonia-free  water  and  testing  with  Nessler. 

10.   Oxygen  required  to  oxidise  the  Organic  Matter. 

Solutions  required : — 

(a)  Standard  solution  of  potassium  permanganate. 

Dissolve  395  parts  of  pure  potassium  permanganate  in  1000  of  water.     Each  c.c. 

contains  -oooi  gramme  available  oxygen. 
(b~)  Potassium  iodide  solution. 

One  part  of  the  pure  salt  recrystallised  from  alcohol,  dissolved  in  10  parts  distilled 

water. 
(c)  Dilute  sulphuric  acid. 

One  part  by  volume  of  pure  sulphuric  acid  is  mixed  with  three  parts  by  volume  of 
distilled  water,  and  solution  of  potassium  permanganate  dropped  in  until  the 
whole  retains  a  very  faint  pink  tint,  after  warming  to  27°  C.  for  four  hours. 
(^/)  Sodium  hyposulphite. 

One  part  of  crystallised  sodium  hyposulphite  dissolved  in  1000  parts  of  water. 
(«.')  Starch  water. 

One  part  of  starch  to  be  intimately  mixed  with  500  parts  of  cold  water,  and  the 
whole  briskly  boiled  for  five  minutes,  and  filtered,  or  allowed  to  settle. 

The  Process. — Two  separate  determinations  have  to  be  made  :  ris.t  the 
.amount  of  oxygen  absorbed  during  15  minutes,  and  that  absorbed  during  four 
'hours  ;  both  are  to  be  made  at  a  temperature  of  27°  C.  It  is  most  convenient 
ito  make  these  determinations  in  i2-oz.  stoppered  bottles,  which  have  been 
irinsed  with  sulphuric  acid  and  then  with  water.  Put  250  c.c.  of  the  water 
linto  each  bottle,  which  must  be  stoppered  and  immersed  in  a  water-bath 
until  the  temperature  rises  to  27°  C.  Now  add  to  each  bottle  10  c.c.  of  the 
dilute  sulphuric  acid,  and  then  10  c.c.  of  the  standard  potassium  permangan- 
.ate  solution.  Fifteen  minutes  after  the  addition  of  the  potassium  perman- 
ganate, one  of  the  bottles  must  be  taken  from  the  bath,  and  two  or  three 
drops  of  the  solution  of  potassium  iodide  added  to  remove  the  pink  colour. 
After  thorough  admixture  add  from  a  burette  the  standard  solution  of  sodium 
hyposulphite,  until  the  yellow  colour  is  nearly  destroyed,  then  introduce  a  few 
•drops  of  starch  water,  and  continue  the  addition  of  the  hyposulphite  until 
the  blue  colour  is  just  discharged.  If  the  titration  has  been  properly  con- 
-ducted,  the  addition  of  one  drop  of  potassium  permanganate  solution  will 
•restore  the  blue  colour.  At  the  end  of  four  hours  remove  the  other  bottle, 


THE  ANALYSIS   OF  WATER,  AIR,   AND  FOOD. 


add  potassium  iodide,  and  titrate  with  sodium  hyposulphite,  as  just  described. 
Should  the  pink  colour  of  the  water  in  the  bottle  diminish  rapidly  during  the 
four  hours,  further  measured  quantities  of  the  standard  solution  of  potassium 
permanganate  must  be  added  from  time  to  time,  so  as  to  keep  it  markedly 
pink.  The  hyposulphite  solution  must  be  standardised,  not  only  at  first,  but 
(since  it  is  liable  to  change)  from  time  to  time  in  the  following  way  : — To 
250  c.c.  of  pure  redistilled  water,  acidulated  with  10  c.c.  acid  as  before,  add 
two  or  three  drops  of  the  solution  of  potassium  iodide,  and  then  10  c.c.  of 
the  standard  solution  of  potassium  permanganate.  Titrate  with  the  hypo- 
sulphite solution,  as  above  described.  The  quantity  used  will  be  the  amount 
of  hyposulphite  solution,  corresponding  to  10  c.c.  of  the  standard  potassium 
permanganate  solution,  and  therefore  representing  i  milligramme  of  oxygen 
consumed.  The  difference  between  the  number  of  c.c.  of  hyposulphite  used 
in  the  blank  experiment  and  that  used  in  the  titration  of  the  samples  of 
water  multiplied  by  the  amount  of  available  oxygen  contained  in  the  perman- 
ganate added  (=  i  milligramme  if  10  c.c.  have  been  used),  and  the  product 
divided  by  the  number  of  c.c.  of  hyposulphite  corresponding  to  the  latter  as 
found  by  the  check  experiment,  is  equal  to  the  amount  of  oxygen  absorbed 
by  the  water. 

Finally,  the  amount  in  milligrammes  of  oxygen  absorbed,  thus  found,  is 
multiplied  by  4  for  parts  per  million,  and  that  result  x  7  and  -f-  100  =  grains 
per  gallon. 

11.   Clark's  Process  for  Hardness.     Total  before  boiling  and  permanent 

after  boiling. 
Solutions,  etc.,  required  :— 

(a)  Standard  solution  of  calcium  chloride. 

Made  by  dissolving  i  gramme  of  pure  calcium  carbonate  in  the  smallest  excess  of 
hydrochloric  acid,  then  carefully  neutralising  with  dilute  ammonia,  and 
making  the  solution  up  to  a  litre  with  distilled  water. 

(b)  Standard  saap  soJu'ion. 

Dissolve  10  grammes  of  air-dried  white  Castile  soap,  cut  into  thin  shavings,  in  a 
litre  of  dilute  alcohol  (sp.  gr.  o  949). 

To  determine  whether  this  solution  contains  the  proper  amount  of  soap,  10  c.c.  of 
the  solution  of  CaCl2  are  diluted  with  60  c.c.  of  water,  and  the  soap  solution 
added  till  a  persistent  lather  forms  on  agitation.  If  n  c.c.  of  the  soap 
solution  have  been  used,  it  has  the  proper  strength.  If  a  greater  or  less 
quantity,  it  must  be  concentrated  or  diluted  to  proper  strength.  The  soap 
solution,  if  turbid,  must  be  shaken  before  using,  but  not  filtered. 

The  Process. — (a)  For  total  hardness.  Put  70  c.c.  of  the  water  into  the 
bottle,  of  250  c.c.  capacity,  and  add  the  soap  solution  gradually  from  a  burette. 
After  each  addition  of  soap  solution,  the  bottle  is  shaken  and  allowed  to  lie 
upon  its  side  five  minutes.  This  is  continued  until,  at  the  end  of  five 
minutes,  a  lather  remains  upon  the  surface  of  the  liquid  in  the  bottle.  At 
this  time  the  hardness  is  indicated  by  the  number  of  c.c.  of  soap  solution 
added,  minus  one.  If  magnesium  salts  are  present  in  the  water  the  character 
of  the  lather  will  be  very  much  modified,  and  a  kind  of  scum  (simulating  a 
lather)  will  be  seen  in  the  water  before  the  reaction  is  completed.  The 
character  of  this  scum  must  be  carefully  watched,  and  the  soap  test  added 
more  carefully,  with  an  increased  amount  of  shaking  between  each  addition. 
With  this  precaution  it  will  be  comparatively  easy  to  distinguish  the  point 
when  the  false  lather  due  to  the  magnesium  salt  ceases,  and  the  true  persistent 
lather  is  produced.  If  the  water  is  of  more  than  16°  of  hardness,  mix  35  c.c. 
of  the  sample  with  an  equal  volume  of  recently  boiled  distilled  water,  which 
has  been  cooled  in  a  closed  vessel,  and  make  the  determination  on  this 
mixture  of  the  sample  and  distilled  water. 


THE  SANITARY  ANALYSIS  OF   WATER.  573 

(b]  For  permanent  hardness.  To  determine  the  hardness  after  boiling,  boil 
a  measured  quantity  of  the  water  in  a  flask  briskly  for  half  an  hour,  adding 
distilled  water  from  time  to  time  to  make  up  for  loss  by  evaporation.  It  is 
not  desirable  to  boil  the  water  under  a  vertical  condenser,  as  the  dissolved 
carbonic  acid  is  not  so  freely  liberated.  At  the  end  of  half  an  hour,  allow  the 
water  to  cool,  the  mcuth  of  the  flask  being  closed  ;  make  the  water  up  to  its 
original  volume  with  recently  boiled  distilled  water,  and,  if  possible,  decant 
the  quantity  necessary  for  testing.  If  this  cannot  be  done  quite  clear,  it  must 
be  filtered.  Conduct  the  test  in  the  same  manner  as  described  above. 

The  hardness  is  to  be  returned  in  each  case  to  the  nearest  half-degree. 

12.  Judging  the  Results. 

No  definite  rule  can  be  laid  down  for  judging  all  the  results  on  one 
uniform  scale,  because  the  analyst  ought  to  have  special  information  as  to  the 
locality,  nature  of  the  soil,  or  depth  of  the  well,  before  giving  an  opinion. 
For  example,  nitrates,  which  have  in  river  and  shallow  surface  waters  the 
highest  significance,  as  indicating  the  presence  of  previous  sewage  contamina- 
tion, entirely  lose  such  force  in  waters  from  deep  artesian  wells,  because  these 
are  naturally  rich  in  such  salts.  The  same  thing  may  be  said  of  ammonia, 
which,  although  highly  unfavourable  in  shallow  waters,  is  yet  always  found  in 
artesian  wells,  most  probably  from  the  metal  pipes  acting  as  reducing  agents 
upon  the  nitrates.  Again,  with  upland  peaty  waters  we  always  find  a  large 
reduction  of  permanganate,  and  consequently  an  excess  of  "oxygen  consumed," 
although  the  organic  matter  so  acting  cannot  be  viewed  as  dangerous. 

Setting  aside,  however,  all  questions  of  mineral  constituents  and  only 
looking  at  the  indications  of  the  presence  or  absence  of  organic  matter,  the 
author  has  devised  a  valuation  scale,  originally  presented  by  him  in  a  paper 
read  before  the  Society  of  Public  Analysts,  and  which  has  proved  since  that 
time  as  nearly  correct  as  any  general  scale  can  be.  The  principle  is  to  divide 
the  amount  of  each  figure  found  in  the  analysis  by  a  fixed  divisor,  and  where 
the  quotient  exceeds  10  to  double  all  figures  over  that  number.  Let  us  suppose 
that,  for  example,  a  water  yielded  '012  grain  of  albuminoid  ammonia  per 
gallon,  and  that  the  divisor  fixed  for  this  indication  is  '0007  ;  then  we  have — 

then  17*1  —  10  —  7'i,  and  7*1x2=  14*2 ; 

therefore  14*2  -f  10  =  24*2,  indicated  degree  of  impurity. 

To  prevent  the  production  of  enormous  figures,  likely  to  startle  non-pro- 
fessional persons,  the  indicated  degree  of  impurity  is  expressed  as  a  decimal 
by  dividing  it  by  100.  Thus,  it  is  only  when  the  article  is  very  bad  indeed 
that  the  indication  comes  into  full  numbers. 

Taking,  then,  the  whole  scale,  it  stands  as  follows  : — 

GRAINS  PER  GALLON. 

Ammonia each  '0015  =  I. 

Albuminoid  Ammonia ,,     -0007  =-=  I. 

Oxygen  consumed  in  15  minutes    .         .  ,,      '004    =  I. 

Oxygen  consumed  in  4  hours  ,,     'oio    =  i. 

PARTS  PER  MILLION. 

Ammonia each  *O2 

Albuminoid  Ammonia   ...  ,,      -oi 

Oxygen  in  15  minutes    .          .         .         .         .  ,,     '057 

Oxygen  in  4  hours          .         .         .         .  ,,      '143 

When  any  number  exceeds  10,  then  all  over  10  is  to  be  doubled  and  added 
to  the  original  number,  and  the  total  valuation  is  to  be  divided  by  100  and 
noted  as  "comparative  degree  of  organic  impurity."  Then,  supposing  w, 


174  THE  ANALYSIS   OF   WATER,   AIR,   AND  FOOD. 

other  consideration  intervenes  to  modify  the  analyst's  opinion  of  the  sample,  the 
following  limits  should  be  observed  : — 

1st  Class  Water up  to  '25  degree. 

2nd     ,,        ,,     (more  or  less  questionable)    .     up  to  '50       ,, 
Undrinkable  Water over   '40       „ 

DIVISION  II.      THE   SANITARY  ANALYSIS   OF  AIR. 

For  definite  sanitary  purposes  it  is  really  necessary  to  make  a  bacteriological 
as  well  as  a  chemical  examination,  but  the  former  being  outside  the  scope  of 
this  book,  only  the  latter  is  considered.  The  chief  points  are  : — 

1.  Testing  for  Gaseous  Impurities. 

The  odour  will  call  attention  to  these  when  present  in  notable  proportions. 
Blotting  paper  dipped  :  (a)  in  tincture  of  turmeric,  and  introduced  into  the 
bottle  containing  the  suspected  air,  turns  red-brown  in  presence  of  ammonia; 
(1})  in  solution  of  subacetate  of  lead — black  with  sulphuretted  hydrogen,  or 
the  vapour  of  ammonium  sulphide ;  (c)  in  solution  of  sodium  nitroprusside— 
purple  with  the  vapour  of  ammonium  sulphide,  but  no  colour  with  H2S  ;  (d} 
in  solution  of  potassium  iodide  mixed  with  starch  paste — blue  with  chlorine 
or  ozone  or  nitrous  acid  ;  (e)  red  litmus  paper  dipped  in  solution  of  potassium 
iodide — blue  with  ozone,  but  not  with  chlorine  or  nitrous  fumes.  A  few  drops 
of:  (a)  weak  solution  of  indigo  introduced  into  the  bottle  is  decolourised  by 
chlorine  and  sulphurous  acid ;  (b)  solution  of  barium  chloride  containing 
nitric  acid  is  rendered  turbid  by  sulphurous  acid;  (c)  solution  of  argentic 
nitrate  is  rendered  turbid  by  chlorine  and  not  by  nitrous  fumes ;  (d)  lime 
water  is  rendered  slightly  turbid  by  ordinary  air,  but  becomes  strongly  milky 
with  air  containing  an  excess  of  carbonic  acid.  Air  which  is  simply  "  foul  " 
from  sewage  impurities  or  overcrowding  will  have  a  very  characteristic 
<;  heavy"  smell,  and  will  decolourise  a  few  drops  of  a  weak  solution  of  potas- 
sium permanganate,  and  will  also  show  an  excess  of  carbonic  acid. 

2.  Estimation  of  Carbon  Dioxide. 

This  is  done  by  the  method  of  Pettenkofer,  which  consists  in  standardising 
100  c.c.  of  lime  (or  baryta)  water  with  standard  oxalic  acid  2-25  grammes  per 
litre,  of  which  i  c.c.  =  'ooi  (i  milligramme  of  CaO).  The  air  to  be 
examined  having  been  collected  in  a  large  bottle  of  known  capacity,  100  c.c. 
of  the  same  lime  water  are  added,  the  bottle  is  closed,  and  well  shaken  for 
some  time.  The  CC>2  is  absorbed,  forming  CaCOs.  The  resulting  milky 
liquid  is  allowed  to  settle,  and  50  c.c.  are  drawn  off  clear  and  immediately 
titrated  with  the  same  acid.  The  indicator  is  turmeric  paper,  or  phenol- 
phthalein,  and  the  number  of  c.c.  of  acid  used  is  multiplied  by  2.  The 
difference  between  the  two  titrations  gives  the  amount  of  CaO  precipitated  as 
carbonate  by  the  CC>2  in  the  air,  and  this  is  then  calculated  thus : — 

c.c.  used  x  'ooi  x  44  =  co  nt  in  the  volume  of  air  taken. 

56 

In  strict  analyses,  the  volume  of  air  taken  must  be  corrected  for  observed 
temperature  and  pressure  to  its  volume  at  N.T.P.  Normal  air  contains  about 
•04  per  cent,  of  COs- 

3.  Estimation  of  Organic  Matter. 

A  known  volume  of  air  is  sucked  by  an  aspirator  through  a  specially 
arranged  apparatus  containing  ammonia-free  distilled  water,  and  the  resulting 
liquid  is  analysed  for  "free  "  and  "  albuminoid  "  ammonia  like  a  water. 


THE  ANALYSIS   OF  FOOD.  175 


DIVISION  III.     FOOD  ANALYSIS. 

Here  we  will  only  attempt  to  consider  a  few  of  the  more  commonly  occur- 
ring cases,  always  choosing  the  simplest  and  most  rapid  process. 

1.  Milk. 

(1)  Specific  Gravity.     Take  the  specific  gravity  at  60°  F.     If  not  at  6o°r 
take  the  temperature  and  refer  to  the  annexed  table  to  get  the  true  gravity  at 
60°,  which  will  be  found  in  the  column  opposite  the  observed  gravity  and  under 
the  observed  temperature. 

(2)  Total   Solids.      Heat   a  small   flat  platinum  dish   about    i|    inch    in 
diameter  to  redness,  cool  it  under  the  desiccator,  and  weigh.     Put  in  5  c.c. 
of  the  milk  and  again  weigh.     The  difference  =  milk  taken.     Now  transfer 
to  the  drying  oven  at  100°  C.  for  6  hours,  cool  under  the  desiccator  and  weigh. 
Put  it  back  in  the  oven  for  an  hour,  repeat  the  cooling  and  weighing,  and 
if  the  difference  does  not  exceed  a  milligramme  or  two  it  is  dry;  if  it  does,, 
then  repeat  the  drying.     The  weight  of  the  dish  and  dry  residue  minus  the 
tare  of  the  dish  equals  the  total  solids,  which  x  TOO  and  -f-  by  weight  of  milk 
taken  =  per  cent,  of  total  solids. 

(3)  Fat.     Is  got  by  using    "  Richmond's  milk  slide  rule/'  an  instrument 
constructed  to  automatically  calculate  by  the  following  formula  thus  (T~ 
total  solids  :   G  —  specific  gravity  :  F—  fat)  :— 

T  =  -2$G  +  1-2  F  +  -14. 
Deducting  the  fat  thus  found  from  the  total  solids,  we  get  the  "solids  not  fat? 

In  event  of  the  sample  being  the  least  sour,  or  when  we  are  dealing  with 
absolutely  skimmed  or  "  separated  ?J  milk,  the  rapid  process  above  given  fails. 
It  is  then  necessary  to  extract  the  fat  as  follows  : — 10  grammes  of  the  milk  are 
weighed  in  a  porcelain  dish,  30  grammes  of  plaster  of  Paris  are  stirred  in,  and 
the  whole  is  placed  upon  the  top  of  the  water  bath  and  stirred  occasionally  till 
it  appears  dry.  (When  the  sample  is  sour  2  drops  of  strong  liquor  ammonia 
are  to  be  added  to  the  milk  in  the  dish  before  stirring  in  the  plaster.)  The 
mass  is  well  powdered  and  introduced  into  a  narrow-mouthed  8-ounce  bottle 
with  a  well-fitting  stopper,  and  140  c.c.  of  pure  ether  having  been  rapidly 
poured  in,  the  bottle  is  closed,  shaken  at  intervals  during  two  hours,  and 
finally  set  aside  in  a  cool  place  to  settle  during  the  night.  In  the  morning, 
if  the  plastered  milk  was  not  over-dried,  it  will  be  found  quite  easy  to  pour 
off  70  c.c.  of  the  ether  perfectly  clear  into  a  weighed  flask,  from  which  the 
ether  may  then  be  distilled  off,  and  the  residual  fat  dried  at  100°  C.  and  weighed. 
The  weight  of  fat  found  x  20  =  percentage  of  fat  in  sample.  Some 
analysts  prefer  to  place  the  plastered  milk  in  a  paper  cartridge  and  exhaust 
it  with  ether  in  the  "  Soxhlet's  tube  "  (see  Chap.  I.,  p.  2),  while  others  cause 
the  milk  to  be  soaked  up  into  a  roll  of  blotting  paper,  dried  thereon,  and  then 
extracted  in  the  "  Soxhlet "  with  ether.  This  latter  is  the  official  process  of 
the  British  Society  of  Public  Analysts,  but  with  ordinary  milk  nothing  is  so. 
simple  and  good  as  the  gravity,  solids,  and  formula. 

(4)  Added  Water.     The  limit  for  the  strength  of  milk  is  at  present  based 
upon  that  of  the  poorest  possible  natural  milk.     Average  milk  will  show  : — 

Fat       ...        3-00 
Solids  not  fat         ...         9'co 

Total  12-00 


176 


THE  ANALYSIS   OF   WATER,    AIR,   AND  FOOD. 


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THE  ANALYSIS  OF  FOOD.  177 


If,  however,  a  milk  has  only — 

Fat         ...        30 

Solids  not  fat        .        .         .        8-5 

Total  1 1 -5, 

it  will  not  be  considered  as  definitely  proved  to  be  adulterated.  In  calculating 
the  amount  of  water  added  the  "  solids  not  fat  "  are  used  for  the  basis  of 
calculation  because  they  are  a  fairly  constant  quantity,  the  fat  being  variable. 
The  amount  of  pure  standard  milk  present  in  any  sample  may  be  calculated 
thus  :— 

Solids  not  fat  x  100       0/    f  .„ 

— TT — —        —  =  %  of  pure  milk  present, 

and  the  difference  between  this  result  and  100  is,  of  course,  added  water. 

(5)  Ash.    The  total  solids  in  the  platinum    dish  are  burned    over  a  low 
flame  at  dull  redness  till  quite  white,  and   the  ash  is  weighed.     The  ash 
should  be  about  70  %,  and  it  will  never,  as  a  rule,  fall  below  '67  in  an 
unwatered  milk. 

(6)  Preservatives  are  frequently  added  to  milk,  the  favourite  ones  being 
boric  acid  and  formalin,  which  can  be  detected  as  follows  : — 

(a)  Formalin  (formic  aldehyd,  40  %)  is  detected  by  diluting  the  sample 
in  a  test  tube  with  an  equal  volume  of  water,  and  then  carefully  running  strong 
sulphuric  acid  down  one  side  of  the  tube,  so  that  about  an  inch  layer  of  it 
forms  at  the  bottom.  On  now  gently  agitating  a  violet  shade  will  appear  at 
the  point  of  contact  of  the  two  liquids  if  formalin  be  present. 

(b}  Boric  acid  is  detected  in  the  ash  of  the  milk  by  moistening  with  a  drop 
or  two  of  strong  sulphuric  acid,  then  adding  alcohol  and  setting  it  on  fire, 
when  it  will  burn  with  a  green  flame  in  presence  of  boric  preservative.  To 
estimate  the  quantity  we  evaporate  100  grammes  of  milk  to  dryness,  in  a 
platinum  dish,  with  2  grammes  of  sodium  hydroxide,  and  having  thoroughly 
charred  the  residue  we  treat  it  with  20  c.c.  of  water  and  add  HC1  drop  by 
drop  till  nothing  more  dissolves.  We  then  wash  from  the  dish  into  a  100  c.c. 
flask,  taking  care  not  to  use  more  than  30  c.c.  of  water,  and  we  then  add  *5 
gramme  solid  CaClg.  To  this  we  then  add  a  few  drops  of  phenol-phthalein, 
and  drop  in  10  per  cent,  solution  of  sodium  hydroxide  until  a  slight  pink  is 
produced,  and  then  having  added  25  c.c.  of  lime  water,  we  make  the  whole 
up  to  the  100  c.c.  mark  and  filter  through  a  dry  filter.  To  50  c.c.  of  this 
filtrate  (=  50  grammes  milk)  we  add  N  sulphuric  acid  till  the  colour  is  dis- 
charged, then  add  methyl-orange  indicator,  and  continue  to  add  the  acid  till 
a  faint  pink  is  produced,  and  lastly  we  drop  in  4'  alkali  till  the  liquid  assumes 
the  yellow  tinge.  At  this  stage  all  acids  other  than  boric  likely  to  be  present 
are  in  a  state  neutral  to  phenol-phthalein.  The  solution  having  been  cooled, 
is  mixed  with  some  phenol-phthalein  and  33  %  of  glycerine  (to  set  free  boric 
acid),  and  is  titrated  with  ^  alkali,  each  c.c.  of  which  consumed  =  "0124 
crystallised  boric  acid  in  50  grammes  of  milk,  and  this  x  2  =  per  cent. 

(7)  Sour  Milks  that  will  not  readily  become  homogeneous  should  have  one 
drop  of  liquor  ammon.  fort,  added  to  each  ounce,  before  shaking,  when  a 
sufficiently  fair  sample  will  be  generally  obtainable  for  analysis.     Sour  milks 
are  generally  from  -2  to  '3  too  low  in  the  "  solids  not  fat,"  and  the  results  are 
not  really  properly  comparable  with  those   from  fresh  milk,  so  caution  is 
necessary  in  forming  opinions  on  sour  samples,  unless  the  departure  from  the 
standard  is  very  marked. 

a  12 


178  THE  ANALYSIS  OF   WATER,  AIR,  AND  FOOD. 


2.  Butter. 

The  only  really  serious  adulteration  of  butter  consists  in  mixing  it  with 
other  fats  of  lower  commercial  value.  Such  a  mixture  may  be  legally  sold  if 
labelled  "  margarine." 

The  butter  is  to  be  first  melted  in  a  beaker  on  the  top  of  the  water  bath, 
when  it  will  gradually  separate  with  a  top  layer  of  clear  butter-fat,  and  a 
bottom  one  of  water  and  curd.  If  the  top  layer  of  fat  does  not  become  quite 
clear  it  must  be  filtered  through  a  dry  filter  placed  over  a  beaker  inside  the 
water  oven,  but  it  will  often  clear  sufficiently  to  enable  enough  to  be  poured 
off  without  filtering,  and,  speaking  generally,  the  better  the  butter  the  more 
easily  the  fat  will  clarify. 

Having  thus  got  the  actual  fat  ready  for  analysis  we  counterbalance  a  small 
flask  of  about  250  c.c.  capacity,  and  having  a  mark  at  150  c.c.,  and  weigh  into 
it  5  grammes  of  the  clarified  fat  and  then  add  50  c.c.  of  a  solution  of  potassium 
hydrate  in  alcohol  (S.V.R.)  having  a  strength  of  30  grammes  per  litre  (3  per 
cent.).  The  flask  having  been  closed  by  a  cork  through  which  passes  a 
piece  of  narrow  glass  tube,  its  contents  are  heated  on  the  water  bath,  with 
constant  agitation,  until  the  fat  is  entirely  dissolved.  The  flask  is  then 
attached  to  a  condenser,  and  the  alcohol  entirely  distilled  off.  The  residual 
soap  thus  left  in  the  flask  is  dissolved  in  a  little  hot  water,  and  25  c.c.  of 
diluted  sulphuric  acid  of  5  per  cent,  strength  having  been  added,  the  whole 
is  made  up  by  distilled  water  to  the  150  c.c.  mark.  A  few  fragments  of 
recently  ignited  pipe-clay  having  been  dropped  in,  the  flask  is  connected  to 
a  short  condenser  and  the  contents  distilled  until  the  distillate  measures 
ico  c.c.  This  distillate  is  then  filtered,  and  a  few  drops  of  solution  of 
phenol-phthalein  having  been  added  the  whole  is  titrated  with  decinormal 
solution  of  sodium  hydrate  or  with  vigintinormal  baryta  water,  which  latter 
is  preferred  by  some  analysts  ;  5  grammes  of  pure  butter-fat  thus  treated  yields 
a  distillate  requiring  not  less  thah  25  c.c.  of  decinormal  soda,  while  lard, 
tallow,  and  the  other  solid  animal  fats  do  not  take  more  than  1-5  c.c.  The 
only  fat  coming  anywhere  near  butter  is  cocoa-nut  fat,  which  takes  about 
7  c.c.,  because  it  also  contains  fatty  acids,  volatile  at  the  heat  of  boiling 
water.  To  calculate  the  amount  of  butter  present  in  any  mixture  we  multiply 
the  number  of  c.c.  of  soda  used  by  100  and  divide  by  25.  Certain  excep- 
tional butters  having  been  met  with,  during  the  winter  months,  which  only 
consumed  21  c.c.,  no  definite  expression  of  opinion  can  safely  be  given  unless 
the  article  takes  less  than  that  number  of  c.c.  of  decinormal  soda. 


3.  Taking  the  Alcoholic  Strength  of  Spirits,  Tinctures,  Wines,  Beer,  and 

all  Alcoholic  Liquids. 

If  the  sample  is  simply  one  of  pure  diluted  alcohol  we  ascertain  its  specific 
gravity,  taking  care  that  the  temperature  of  the  liquid  is  exactly  60°  F.  We 
then  look  at  the  annexed  table  and  find  the  strength  of  the  spirit.  It,  how- 
ever, frequently  happens  that  it  is  not  possible  to  get  the  sample  exactly  to 
60°  F.,  and  in  such  a  case  we  must  carefully  note  the  temperature  at  which 
;ve  worked  and  make  a  calculated  correction  for  the  expansion  of  the  spirit, 
based  on  the  following  data  : — 

If  the  spirii  be  above  70  per  cent,  of  apparent  strength,  then  we  must  add 
•0005  to  the  specific  gravity  for  each  degree  F.  that  the  spirit  was  above 


(3)  Table  for  ascertaining  the  percentages  respectively  of  Alcohol   by 
Weight,  by  Volume,  and  as  Proof  Spirit,  from  the  Specific  Gravity. 


Specific 

K'F'. 

Absolute 
Alcohol 
:>y  Wght 
Per  cent. 

Absolut 
Alcoho 
by  vol'm 
Per  cen 

Proof 
Spirit. 
Per  cent 

Specific 
gravity, 
at  60°  F. 

Absolute 
Alcohol 
by  w'ght 
Per  cent 

Absolute 
Alcohol 
by  vol'mc 
Per  cent 

Procf 
Spirit. 
Per  ctn. 

Specific 
gravity, 
at  60°  F. 

Absolute 
Alcohol 
>.y  w'ght 
Per  cent 

Absolut 
Alcohol 
by  vol'm 
Per  cen 

Proof 

Spirit. 
Per  cent. 

I  '000 

000 

O'OO 

OO 

•928 

45-50 

53-I5 

93'2 

•859 

75-50 

8l70 

I43-2 

•999 

0'55 

0-65 

O'l 

•927 

45-95 

53-65 

94-1 

•858 

75^0 

81-95 

143-8 

•998 

1-05 

I-30 

2'4 

•926 

46-40 

54'10 

94-8 

•857 

76-30 

82-40 

144-4 

•997 

1-60 

2'OO 

3'5 

•925 

46-90 

54'60 

95-6 

•856 

76-70 

8275 

M50 

•996 

2T5 

2-70 

4'9 

•924 

47-30 

55'10 

96*5 

•855 

77-15 

83-I5 

145-6 

•995 

275 

3'5o 

6-1 

•923 

47-80 

55-55 

97-4 

•854 

77-55 

83-45 

I46-2 

•994 

3'3Q 

4-i5 

7-2 

•922 

48-25 

56-05 

98-2 

•853 

78-00 

83-80 

146*7 

•993 

3-90 

4-90 

8-6 

•921 

48-65 

56-50 

99-o 

•852 

78-40 

84-I5 

147-4- 

•992 

4-50 

5-65 

9'9 

•920 

49-I5 

56-95 

99-8 

•85I 

78-80 

84-45 

I48-0 

'GOT 

p-ie 

6'jd.o 

1  1"2 

"850 

7Q'2O 

84-84 

i/iS-f> 

yy  i 
•990 

J  1J 

575 

7-15 

12-6 

•9198   !  49-25 

57-05      loo-oPS 

•849 

/y  ^u 
79-60 

85-I5 

1  40  t> 

149-1 

•oSo 

f\"  A  d 

X-nn 

_ 

1 

1                      II      .0.0 

8o-oc 

8c-cn 

yoy 
•988 

U  a^\J 

7-10 

o  OO 

8-80 

14  1 

iS'S 

•919 

49'65 

57-40 

ioG-6 

*-7^<J 

•847 

OU  U^) 

80-45 

o5   5 

85-90 

!497 
150-3 

•987 

7-80 

9-65 

16-9 

•918 

5O-IO 

57-90 

101-5 

•846 

80-80 

86-15 

150-9 

•986 

8-50 

1<>'SS 

18-4 

•917 

50-55 

58-40 

102-3 

•845 

81-20 

86-50 

IS1'5 

•985 

9-20 

11-40 

20  -o 

•9l6 

5I-OO 

58-85 

103-1 

•844 

81-65 

86-80 

152-1 

•984 

9-90 

!2'35 

21-5 

•915 

5^45 

59-30 

103-9 

•843 

82-00 

87-10 

1527 

•983 

10-65 

13-20 

23-1 

•914 

5I-90 

59-75 

104-7 

•842 

82-45   87-45 

153-2 

•982 

1  1  '45 

14-10 

247 

•913 

52-35 

60-15 

105-5 

•84I 

82-80   87-75 

I53-8 

•98l 

12-25 

15-10 

26-5 

•912 

52-80 

60'6S 

106-5 

•840 

83-20 

88-05 

I54-3 

•980 

13-00 

16-00 

28-0 

•911 

53-25 

5I-05 

107-0 

•839 

83-60 

88*35 

I54-9 

'979 

13-80 

17-00 

29-8 

-9IO 

53-65 

6r50 

107-8 

•838 

8400 

88-65 

!55'4 

•978 

H'SS 

18-00 

31-6 

•909 

54'10 

6l'95 

108-5 

•837 

84-40 

89-00 

156-0 

'977 

I5-45 

19-00 

33-3 

•908 

54-55 

62*40 

109*3 

•836 

84-80 

89-30 

156*5 

•976 

16-30 

20-00 

35  -i 

•907 

54^5 

62-80 

IIO'O 

•835 

85-20 

89-60 

157-1 

'975 

17-10 

21-00 

36-8 

•906 

55-45 

63-30 

110-9 

•834 

85-60 

8995 

I57-6 

"974 

17-90 

21-95 

38-5 

•905 

55-90 

63-70 

ni'6 

•833 

85-95 

90-25 

158*1 

'973 

18-80 

23-05 

40-5 

•904 

56-35 

64-10 

112-3 

•832 

86-35 

90-55 

158-6 

•972 

I9-55 

23-90 

42-0 

•903 

56-75 

64-55 

113-1 

•831 

86-75 

90-85 

i59-i 

•971 

20-35 

24-90 

43'6 

•902 

57-20 

65-00 

113-9 

•830 

87-15 

91-10 

I59-7 

•970 

2TIO 

2575 

45'2 

•9OI 

57^0 

65-35 

114-6 

•829 

87-50 

91-40 

160-2 

•969 

21-95 

26-85 

46-9 

•900 

58-05 

65-80 

II5-4 

•828 

8790 

91-70 

160-7 

•968 

2275 

27-75 

48-6 

•899 

58*55 

66-30 

Il6'2 

•827 

88-30 

92-00 

161-2 

•967 

23-5° 

28-65 

50-2 

•898 

58-95 

66-65 

116-8 

•826 

88-65 

92-30 

161-7 

•966 

24-25 

29-55 

51-8 

•897 

59-35 

67-05 

117-5 

•825 

8905 

92*55 

162-2 

•965 

25-00 

30-40 

53-3 

•896 

59-85 

67-55 

1184 

•824 

89-50 

92-90 

162-8 

•964 

25-70 

31-20 

54-7 

•895 

60-30 

68-00 

119*2 

•823 

89-90 

93-25 

163-4 

•963 

26-45 

32-05 

56-2 

•894 

60-70 

68-35 

119-8 

•822 

90-25 

93-50 

163-9 

•962 

27-I5 

3290 

57-6 

•893 

6rio 

68-75 

120-5 

•821 

9065 

93-75 

164-3 

•961 

27-80 

3360 

59'0 

•892 

6i-55 

69-15 

I2I'I 

•820 

9095 

94-00 

164-7 

•960 

28-45 

34'40 

60-3 

•89I 

62-00 

69-96 

I21'9 

•8l9 

9I-35 

94-25 

165-1 

959 

29-10 

35-10 

6r6 

•890 

62-45 

69-95 

I22'6 

•8l8 

9170 

94-5° 

165-6 

•958 

2970 

35-8o 

62-8 

•889 

62-85 

70-35 

123*3 

*8l7 

9205 

94-75 

1  66-  1 

'957 

30-35 

36-55 

64-1 

-888 

63-25 

70*75 

124-0 

•816 

92*45 

95-00 

166-5 

•956 

31-00 

37'35 

65-4 

•887 

63-70 

71-20 

124-7 

•815 

92-80 

95-25 

167  o 

'955 

31-55 

37'95 

66-5 

•386 

64-15 

71-60 

I25-4 

•814 

93-20 

95-50 

167-4 

'954 

32-I5 

38-60 

67-6 

•885 

64-55 

71-90 

126-0 

•813 

93-55 

95*80 

167-9 

'953 

3270 

39'2o 

68-7 

•884 

65-00 

72-35 

126-3 

•812 

93-95 

96-10 

168-4 

•952 

33-30 

39-90 

700 

•883 

65-40 

72*75 

127-5 

•811 

94-3° 

96*35 

168-8 

•95i 

33'SO 

40-55 

71-0 

•882 

65-80 

73-I5 

128-2 

•810 

94-60 

9655 

169-2 

•950 

34-40 

41-20 

72-2 

•881 

66-25 

73-50 

I28-9 

•809 

94-95 

96-80 

169-6 

•949 

35-00 

41-85 

73-3 

•880 

66-65 

73-90 

129-6 

*3o8 

95-3° 

97-05 

170-0 

•948 

35-50 

42-40 

74-3 

•879 

67-05 

74-3° 

I30-2 

•807 

95-70 

97-25 

170-4 

'947 

36-05 

43-00 

75-4 

•878 

67-55 

74-70 

130-9 

•806 

96-00 

97-50 

170-8 

•946 

36-55 

43-60 

76-4 

•877 

67-95 

75-10 

I3r6 

•805 

96-35 

97-70 

171-2 

'945 

37-10 

44-I5 

77-4 

.876 

68-40 

75-45 

I32-2 

•804 

96-70 

97-95 

171-6 

'944 

37-65 

44-75 

78-4 

•875 

68-80 

75-8o 

132-9 

•803 

97-03 

98-15 

172-0 

•943 

38-20 

45-40 

79-5 

•874 

69-20 

76-15 

I33-5 

•802 

97-35 

98-40 

172-4 

•942 

38-65 

45^5 

80-4 

•873 

69-65 

76-60 

I34'3 

•801 

97-70 

98-55 

172-7 

•941 

39-I5 

46-40 

81-4 

•872 

70-05 

76*95 

I34-9 

•800 

98*00 

98*75 

173-i 

•940 

39-70 

47-00 

82-4 

•871 

70-50 

7735 

1  35  '6 

"799 

98-35 

99-00 

I73-5 

•939 

40-15 

47-50 

83-3 

•870 

70-85 

77-65 

136-1 

•798 

98-65 

99-20 

173-8 

•938 

40-65 

48-05 

84-1 

•869 

71-30 

78-10 

136-6 

797 

98-95 

99-40 

174*1 

•937 

4I-I5 

4860 

85-1 

•868 

71-75 

78-45 

I37-4 

796 

9930 

99-55 

174-4 

•936 

41-65 

49-10 

86-1 

•867 

72-20 

78-75 

138*1 

"795 

99-60 

99-75 

1748 

•935 

42-15 

49'65 

87-0 

•866 

72-55 

79-I5 

138-8 

794 

99'95 

99-95 

175-2 

'934 

4265 

5°'  1  5 

87-9 

•865 

73-00 

79-55 

I39-4 

'933 

43-I5 

50-70 

889 

•864 

73-45 

7995 

140-1 

•932 

43-6o 

51-20 

89-8 

•863 

73-80 

80-25 

140-7 

Absolute  Alcohol. 

•93i 

44-10 

51-70 

90-6 

•862 

74-25 

80-60 

141-3 

•020 

A  A  '  C  C 

rii  'A 

•86  1 

*7  A  '  7O 

S  i  *oo 

T  A  T  Tl 

yju 
•929 

44  33 
45-00 

52-I5 
5270 

yi  4 

92-3 

•860 

/4  /u 

75-10 

81*35 

141  y 
I42-6 

7938 

roo-oo 

lOO'OO 

I75-2S 

i8o  THE  ANALYSIS  OF   WATER,   AIR,   AND  FOOD. 

60°  F.,  or  we  must  deduct  the  same  amount  for  each  degree  that  the  spirit- 
was  below  60°.  This  will  now  give  the  real  gravity  at  60°  F.,  and  a  reference 
to  the  table  will  show  the  true  strength.  If  the  spirit  is  below  70  per  cent., 
we  must  then  use  smaller  amounts  to  add  or  deduct  as  follows  :- 

Under  70  but  over  40  add  or  deduct  '0004  for  each  degree  F. 

,,       40       „         25  „  -0003          ,, 

„       25       ,,         15  ,,  -0002 

15       »          °  t»  'C001          »»          »» 

When  we  are  operating  on  a  wine,  tincture,  or  other  complex  alcoholic 
liquor,  the  spirit  it  contains  must  be  distilled  off  and  the  specific  gravity 
of  the  distillate  ascertained.  To  do  this  we  take  50  c.c.  of  the  sample,  and 
having  carefully  taken  its  temperature  and  noted  the  same,  we  transfer  it  to 
a.  small  retort  attached  to  a  condenser,  rinsing  out  the  measuring  flask  with 
two  successive  quantities  of  5  c.c.  each  of  distilled  water.  We  then  place  the 
same  measuring  flask  at  the  end  of  the  condenser  and  distil  until  40  c.c.  have 
passed  over.  10  c.c.  of  distilled  water  are  now  to  be  added  to  the  contents 
of  the  retort,  and  the  distillation  is  to  be  continued  until  very  nearly  50  c.c. 
have  been  distilled  over.  The  temperature  of  this  distillate  having  been 
brought  to  the  same  degree  as  that  at  which  the  sample  was  measured, 
distilled  water  is  to  be  added  exactly  up  to  the  50  c.c.  mark.  By  this  means 
it  is  possible  to  obtain  a  volume  of  pure  spirit  of  precisely  the  same  strength 
as  the  sample,  and  we  finally  take  the  specific  gravity  of  the  same  and  apply 
the  tables  as  above  directed.  Some  chemists  prefer  to  distil  off  three-fourths 
of  the  sample,  and  having  taken  the  specific  gravity  of  the  distillate,  to  add 
some  water  and  distil  off  the  remaining  fourth,  taking  its  gravity  separately, 
and  finally  adding  the  results  both  together. 

4.  Bread  and  Flour. 

Take  10  grammes  of  the  bread  in  a  weighed  platinum  dish,  and  dry  it  in  the 
water  oven  for  3  hours  at  a  temperature  of  100°  C.  Good  bread  should  not 
lose  more  than  44  per  cent,  of  its  weight.  Now  place  the  dish  over  the  Bunsen 
burner  and  heat  it  to  redness  until  it  is  reduced  to  a  uniformly  greyish-white 
ash  and  again  weigh.  This  ash  should  not  weigh  more  than  1*5  per  cent,  of 
the  original  bread. 

Note. — Both  bread  and  flour  are  very  difficult  to  burn,  and  it  is  better  to  first  char  them  to 
a  mass  of  coke,  then  to  remove  this  mass  to  a  glass  mortar  and  powder  it,  and  finally  to 
return  the  powder  to  the  platinum  dish  to  finish. 

Acidity.  Put  20  grammes  of  bread  (or  10  grammes  of  flour)  into  an  8-oz. 
wide-mouthed  stoppered  bottle,  and  pour  in  200  c.c.  of  rectified  spirit ;  close 
the  bottle  and  let  it  stand  some  hours.  Then  pour  off  100  c.c.  of  the  clear 
liquor,  add  a  drop  of  solution  of  phenol-phthalein  and  run  in  decinormal 
solution  of  soda  until  a  pink  tint  is  produced.  Good  fresh  bread  or  flour 
should  not  require  more  than  i  c.c.  of  the  soda  solution  to  render  it  alkaline. 

Alum.  Mix  together  5  c.c.  of  freshly  prepared  tincture  of  logwood  with 
5  c.c.  of  a  saturated  solution  of  official  carbonate  of  ammonia  .ind  50  c.c.  of 
water,  and  at  once  pour  it  on  to  a  mass  of  the  bread  taken  from  the  inner 
portion  of  the  loaf.  If  a  fair  adulteration  of  alum  be  present  a  slate-blue 
colour  will  be  produced,  but  if  the  amount  of  alum  be  small  (say  less  than  10 
grains  per  4-lb.  loaf)  then  the  colour  will  only  appear  after  gently  warming  on 
the  top  of  the  water  oven  for  some  time.  If  the  presence  of  alum  be  shown 
by  this  test,  its  amount  must  be  estimated  as  follows  : — 100  grammes  of  the 
bread  are  burned  to  ash  in  a  platinum  dish,  and  when  cold  5  c.c.  of  fuming 
hydrochloric  acid  are  added,  and  the  dish  having  at  once  been  covered  by  a 
glass  plate  the  whole  is  allowed  to  stand  for  15  minutes;  25  c.c.  of  water  are 


THE  ANALYSIS  OF  FOOD.  181 

then  added  to  the  dish  and  its  contents  are  gently  boiled  for  five  minutes  and 
filtered.  The  insoluble  matter  (chiefly  silicious  matter  and  clay)  having  been 
washed  and  the  washings  added  to  the  filtrate,  the  latter  is  mixed  with  5  c.c. 
of  strong  liquor  ammonias  and  40  c.c.  of  acetic  acid.  The  ash  of  bread 
being  rich  in  phosphoric  acid,  the  precipitate  thus  produced  will  consist  of 
aluminium  phosphate  with  some  ferric  phosphate;  and  such  precipitate  must 
then  be  filtered  off,  washed,  dried,  ignited,  and  weighed.  If  this  precipitate 
does  not  exceed  5  milligrammes  it  is  not  worth  going  farther,  but  if  it  does, 
we  must  then  proceed  to  estimate  the  iron  present  in  it  by  the  colouri metric, 
method  given  at  page  126.  The  ferric  chloride  solution  used  should  contain 
an  amount  of  iron  equivalent  to  one-tenth  of  a  milligramme  of  ferric  phosphate 
in  each  c.c.  After  the  iron  has  been  estimated  and  deducted  from  the 
original  weight  of  the  precipitate,  each  milligramme  remaining  may  be  taken, 
as  representing  one  grain  of  alum  per  4-lb.  loaf. 

Alum  and  other  mineral  impurities  added  to  flour  are  best  detected  by 
shaking  up  some  of  the  sample  with  chloroform  in  a  separatory  funnel,  and 
then  letting  it  stand,  when  the  flour  will  float  on  the  top,  and  the  sand,  alum,, 
and  other  mineral  matters  will  sink  to  the  bottom. 

5,   Mustard. 

This  is  chiefly  a  microscopical  matter  for  the  exact  identification  of  impuri- 
ties, but  the  following  chemical  operations  may  be  performed  :— 

(1)  Test  a  cooled  decoction  for  starch  with  solution  of  iodine. 

(2)  If  starch  be  found,  extract  a  weighed  portion  in  the  "  Soxhlet " 

with  petroleum  spirit  or  ether.  Distil  off  the  spirit,  dry  and 
weigh  the  oil.  Mustard  contains  as  an  ordinary  minimum 
33  %  of  oil,  and  the  amount  of  genuine  mustard  in  the  sample, 
will  then  be  found  thus  : — 


%  of  oil  found   x    100 


33 


~~  %  genuine  mustard  J 


by  deducting  this  from  100  the  difference  is  added  starch  or 
flour. 

(3)  Moisten  the   mustard  with  a  little  ammonia,  when   the  turmeric 
broy'Li  will  be  developed  if  that  colouring  agent  be  present. 

6.  Pepper. 

Mineral  Impurities.  Weigh  out  10  grammes  of  the  sample  in 'a  tared 
platinum  dish  and  ignite  it  to  a  perfect  ash,  as  already  described  under  bread, 
and  weigh.  If  the  ash  does  not  much  exceed  2  per  cent,  in  white,  or  5  per 
cent,  in  black  pepper,  it  may  be  passed,  but  if  it  does,  the  contents  of  the 
dish  must  be  boiled  with  diluted  hydrochloric  acid,  and  the  insoluble  matter 
having  been  collected  on  a  filter,  and  washed  until  free  from  acidity,  is  to 
be  dried,  ignited,  and  weighed.  Any  insoluble  matter  thus  found  over  4-5 
per  cent,  may  be  considered  to  represent  adulteration  with  sand. 

Vegetable  Impurities.  These  are  rendered  visible  under  the  microscope 
by  mounting  some  of  the  sample  with  a  drop  of  an  acid  solution  of  aniline 
acetate,  which  stains  poivrette  (ground  olive  stones)  and  other  woody  im- 
purities yellow,  without  affecting  the  detection  of  any  rice  flour  or  other  cereal 
that  may  be  present.  If  they  be  found  we  can  get  a  fair  idea  of  their  amount 
by  estimating  the  amount  of  matter  soluble  in  alcohol  (resin,  piperine,  etc.),, 
present  in  the  sample  as  follows  :— 2  grammes  of  the  pepper  are  boiled  in  a  long- 


182  THE  ANALYSIS  OF   WATER,   AIR,   AND  FOOD. 

necked  flask  with  40  c.c.  of  absolute  alcohol  for  ten  minutes  and  the  solution 
passed  through  a  filter  placed  over  a  large  platinum  dish,  the  insoluble  matter 
on  the  filter  being  washed  with  another  25  c.c.  of  alcohol.  The  dish  is 
placed  on  the  water  bath  until  the  spirit  has  passed  off,  and  the  residue  is 
dried  for  half  an  hour  at  100°  C.  and  weighed.  Lastly,  it  is  placed  over  the 
"  Bunsen  "  and  ignited,  cooled,  and  again  weighed,  and  the  weight  deducted 
from  the  former  one.  The  difference  is  the  weight  of  the  extract,  which 
should  not  be  less  than  8  per  cent,  in  white,  or  10  per  cent,  in  black  pepper. 
If,  for  example,  the  extract  of  a  sample  of  white  pepper,  in  which  rice  starch 
had  been  found  by  the  microscope,  only  amounted  to  4  per  cent.,  we  should 
then  charge  it  with  being  adulterated  to  the  extent  of  50  per  cent. 

In  the  case  of  poivrette  or  excessive  bleached  pepper  husk  being  found  in 
a  sample,  we  boil  one  gramme  for  an  hour  with  100  c.c.  of  water,  and  2  c.c.  of 
sulphuric  acid  under  an  upright  condenser  for  an  hour,  cool  and  filter  through 
a  pair  of  counterbalanced  filters,  wash  till  every  trace  of  acidity  has  been 
removed,  and  dry  the  filters  and  their  contents  to  constant  weight  in  the 
water  oven.  Pure  pepper  thus  treated  yields  not  more  than  35  per  cent,  of 
insoluble  matter,  while  husks  and  poivrette  yield  70  and  75  per  cent,  respec- 
tively. The  calculation  is  manifest  —  thus,  suppose  a  sample  (in  which  much 
husk  was  seen  under  the  microscope)  to  show  52-5  per  cent,  of  insoluble 
matter,  it  would  contain  50  per  cent,  of  added  husks.  A  not  uncommon 
recent  adulteration  of  pepper  consists  in  adding  ground  ginger  which  has  been 
already  exhausted  by  spirit  to  make  the  essence  of  ginger. 

7.  Coffee, 

If  chicory  be  found  by  a  microscopic  examination  of  the  sample  —  best  done 
after  boiling  with  dilute  NaHO  —  10  grammes  of  the  coffee  are  placed  in  a 
flask  with  100  c.c.  of  distilled  water.  The  flask  is  counterbalanced,  and  then 
boiled  for  a  quarter  of  an  hour.  It  is  then  placed  on  the  scales,  and  the 
original  balance  is  restored  by  adding  water.  Finally  the  decoction  is  filtered, 
cooled  to  1  5  '5°  C.,  and  its  specific  gravity  is  taken.  The  gravity  of  pure  coffee 
does  not  exceed  1009-5,  while  that  of  chicory  solution  is  10217.  Supposing, 
therefore,  that  a  decoction  showed  a  gravity  of  1015  '5,  then  — 


10217  —  Ioo9'5  =  I2'2,  and  ioi5'5  —  1009*5  =  6*0 
therefore  — 

I2'2  :  6  ::  100  =  49  per  cent,  of  chicory. 

8.  Colored  Sweets. 

The  poisonous  colors  are  nearly  all  mineral  and  insoluble.  They  may  be 
scraped  off,  washed  with  water,  and  identified  by  the  ordinary  methods  given 
in  Chapter  IV.  As  a  rule,  at  present,  only  aniline  colors  are  used,  and  they 
are  added  in  such  minute  proportions  as  not  to  be  considered  dangerous. 

9.  Free  Sulphuric  Acid  in  Vinegar. 

To  a  dilute  solution  of  methyl  violet  add  a  drop  of  vinegar.  A  blue  colour 
shows  the  presence  of  a  mineral  acid  in  the  sample. 

Mix  50  c.c.  of  the  vinegar  with  25  c.c.  of  volumetric  solution  of  sodium 
hydrate,  made  decinormal  by  diluting  the  normal  volumetric  solution  to  ten 
times  its  bulk  with  water.  The  whole  is  evaporated  to  dryness,  and 
incinerated  at  the  lowest  possible'  temperature.  25  c.c.  of  decinormal  solution 
of  oxalic  acid  (made  to  exactly  balance  the  sodium  hydrate  solution)  are 


THE  ANALYSIS   OF  FOOD.  183 

now  added  to  the  ash,  the  liquid  heated  to  expel  CO2,  and  filtered.  The 
filter  is  washed  with  hot  water,  and  the  washings  having  been  added  to  the 
filtrate,  phenol-phthalein  solution  is  added,  and  the  amount  of  free  acid  ascer- 
tained by  running  in  decinormal  soda  from  a  burette.  The  number  of  c.c. 
of  soda  thus  used  multiplied  by  '0049  giyes  tne  amount  of  free  sulphuric  acid 
in  the  vinegar.  This  process  depends  on  the  fact  that  whenever  the  ash  of 
vinegar  has  an  alkaline  react  ion,  free  mineral  acid  was  undoubtedly  absent. 


CHAPTER    XL 

ANALYSIS  OF  DRUGS,  FIXED  AND  ESSENTIAL  OILS, 
FATS,  WAXES,  SOAPS,  DISINFECTANTS,  URINE,  AND 
URINARY  CALCULI. 


DIVISION   I.     ANALYSIS    OF    DRUGS, 

I.  GENERAL  SCHEME. 

THE  analysis  of  drugs  is  so  large  a  subject  that  only  a  few  of  the  more 
commonly  occurring  problems  can  be  discussed  in  the  present  volume.  It 
will,  however,  be  interesting,  before  proceeding  to  the  consideration  of  special 
matters,  to  give  a  sketch  of  the  general  method  of  analysing  a  vegetable  sub- 
stance used  in  medicine,  following  the  lines  laid  down  by  Dragendorff. 

Step  I,  Dry  a  weighed  portion  of  the  substance  in  the  water  oven  until  it 
ceases  to  lose  weight. 

Step  II,  Pack  the  dried  and  powdered  substance,  mixed  with  a  little 
sand,  in  a  "  Soxhlet "  apparatus,  thoroughly  exhaust  it  with 
petroleum  spirit,  and  cork  up  and  save  the  fluid  extract  so 
obtained,  marking  it  A. 

Step  III.  Spread  the  solid  left  from  Step  II.  out  to  dry  on  a  plate  of  glass 
on  the  top  of  the  water  oven,  and  when  all  odour  of  petroleum 
has  passed  off,  replace  it  in  the  Soxhlet,  and  exhaust  it  this  time 
with  perfectly  anhydrous  ether.  Cork  up  the  ethereal  extract 
obtained  and  mark  it  B. 

Step  IV.  Spread  out  as  before,  and  when  all  odour  of  ether  is  gone  re-pack 
and  extract  with  purified  commercial  methyl  alcohol,  as  sold  for 
making  methylated  spirit.  This  is  more  volatile  than  common 
alcohol,  and  is  as  a  rule  a  better  solvent  of  the  articles  required 
in  this  group,  while  it  does  not  so  readily  extract  glucose,  etc. 
It  is  an  article  of  commerce,  and  can  be  specially  ordered 
through  a  purveyor  of  chemicals  as  "  commercial  methol,  highest 
strength."  Save  this  alcoholic  extract  and  mark  it  c. 

Step  V.  Extract  the  insoluble  matter  from  Step  IV.  with  distilled  water 
at  a  temperature  not.  exceeding  120°  Fahr.,  and  filter.  Wash 
with  cold  water  and  save  the  filtrate  (D). 

Step  VI.  Wash  the  insoluble  matter  off  the  filter  into  a  large  flask,  with 
plenty  of  water,  acidulated  with  i  per  cent,  of  hydrochloric  acid, 
and  boil  it  for  an  hour  under  an  upright  condenser.  Let  it  settle, 
pour  off  the  liquid  as  close  as  possible  (saving  it),  and  then 
collect  the  insoluble  matter  on  a  filter  and  wash  with  boiling 
water,  adding  the  washings  to  what  was  poured  off.  This  extract 
is  marked  E. 

184 


GENERAL    SCHEME.  185 


Step  VII.  Once  more  wash  the  insoluble  matter  from  the  filter  into  a  beaker 
and  boil  it  up  for  an  hour  with  plenty  of  water  rendered  distinctly 
alkaline  with  sodium  hydrate.  Collect  on  a  weighed  filter,  wash 
first  with  boiling  water,  acidulated  with  hydrochloric  acid,  and  then 
with  plain  boiling  water,  till  no  trace  of  a  chloride  remains ;  dry 
in  the  water  oven  and  weigh,  deducting  the  tare  of  the  filter. 
Lastly,  ignite  the  filter  and  its  contents  in  a  weighed  platinum 
basin,  and  deduct  the  ash  so  found  from  the  first  weight,  and  the 
difference  will  be  a  woody  fibre  in  the  drug. 

Step  VIII.  Make  a  nitrogen  determination  by  KjeldahPs  method  (page  166) 
on  a  fresh  portion,  and  the  nitrogen  found  (after  deducting  any 
due  to  alkaloids  present)  multiplied  by  6^33  will  give  the  amount 
of  albuminous  bodies  present. 

Treatment  of  the  Separate  Solutions. — Each  liquid  is  made  to  a  definite 
number  of  c.c.  with  the  same  solvent,  and  then  an  aliquot  part,  say 
10  c.c.,  is  taken  and  evaporated,  and  the  residue  weighed,  to  find  the  total 
matter  soluble  in  each  solvent.  The  remainders  of  the  liquids  are  then  treated 
as  follows  : — 

Liquid  A.  This  will  contain  chiefly  fixed  and  volatile  oils.  The  spirit  is 
allowed  to  evaporate  spontaneously,  or  in  a  current  of  cold  dry 
air,  and  the  residue  is  distilled  with  water,  when  the  volatile  oil 
passes  over,  leaving  the  fixed  oil  in  the  retort. 

Liquid  B.  This  chiefly  contains  resins,  together  with  some  bitters,  alkaloids, 
and  organic  acids.  The  solution  is  evaporated  to  dryness  on  the 
water  bath  with  sand,  and  the  residue,  having  been  powdered, 
is  boiled  with  water  slightly  acidulated  with  HC1.  A  portion 
of  this  watery  solution  is  tested  for  benzoic,  cinnamic,  salicylic, 
gallic,  and  other  free  organic  acids,  and  the  remainder  is  saved 
for  subsequent  use  in  Group  C.  The  portion  insoluble  in  water 
now  chiefly  represents  any  resins  present  in  the  drug,  which  are 
soluble  in  ether.  These  may  be  further  divided  and  examined 
by  the  action  of  alcohol.  Resins  are  recognised  by  their 
behaviour  with  solvents,  their  odour  on  warming,  and  by  the 
action  of  H2SO4,  HNOs,  HC1,  etc.,  on  spots  of  the  solid  resin 
left  by  evaporating  the  solutions.  This  matter  requires  special 
experience ;  but  a  description  of  the  nature  and  reactions  of  all 
the  principal  resins  will  be  found  in  any  large  book  on  Materia 
Medica. 

Liquid  C.  Is  evaporated  to  a  low  bulk,  and  then  poured  into  water  faintly 
acidulated  with  hydrochloric  acid.  Any  insoluble  matter  is 
probably  a  resinous  body  insoluble  in  ether,  and  is  to  be 
filtered  out  and  examined  as  a  resin.  A  portion  of  the  aqueous 
solution  is  to  be  tested  for  tannin,  and  the  remainder  is  to  be 
mixed  with  the  reserved  liquid  from  B,  the  whole  gently  evaporated 
to  a  convenient  bulk,  and  treated  by  immiscible  solvents  as 
follows : — 

Step  I.  The  liquid  (which  must  still  retain  a  slightly  acid  reaction)  is 
shaken  up  successively  with  chloroform  and  ether  in  a  separator 
(see  fig.  17,  page  93).  The  solvents  are  drawn  off  and  evapo- 
rated, and  the  residues  so  obtained  tested  for  glucosides  and 
bitter  principles. 


1 86  ANALYSIS   OF  DRUGS,   ETC. 

Step  II.  The  liquid  remaining  in  the  separator  is  now  rendered  alkaline 
with  sodium  hydrate  and  again  shaken  up  with  chloroform. 
This  extracts  nearly  all  the  alkaloids.  The  chloroform  is 
evaporated  and  the  residue  tested  for  alkaloids  (see  Chap.  V.). 

Step  III.  The  liquid  still  remaining  in  the  separator  is  shaken  up  with 
warm  amylic  alcohol,  which  takes  out  morphine  and  leaves  it 
on  evaporation,  when  any  residue  is  tested  for  its  presence. 

Liquid  D,  Is  evaporated  to  a  low  bulk  and  then  mixed  with  twice  its 
volume  of  rectified  spirit,  when  gums  precipitate  insoluble  and 
may  be  examined,  and  sugars  dissolve  and  may  be  estimated  by 
"  Fehling."  Saponin  also  may  be  found  with  the  sugars. 


II,  ALKALOIDAL   ASSAY    BY    IMMISCIBLE    SOLVENTS. 

The  immiscible  solvents  usually  employed  in  the  assay  of  alkaloids  are 
chloroform,  ether,  benzin  (petroleum  spirit),  benzol  (benzene),  and  amylic 
alcohol,  or  a  mixture  of  the  latter  two  called  benzolated  amylic  alcohol.  The 
liquids  are  not  miscible  with  water,  but  can  be  diffused  through  it  by  shaking, 
and  then  separate  from  it  when  set  at  rest.  It  is  a  general  property  of 
alkaloids  that  they  themselves  are  as  a  rule  soluble  in  all  the  above  solvents, 
while  their  salts  are  insoluble.  If,  therefore,  we  start  with  an  acid  aqueous 
solution  of,  say,  quinine  sulphate,  and,  having  added  sufficient  alkali  to  set 
free  the  quinine,  we  shake  up  with  chloroform,  and  then  leave  the  latter  to 
settle,  the  chloroformic  layer  will  contain  all  the  alkaloid.  If  we  then  run 
off  this  layer  and  shake  it  up  with  diluted  sulphuric  acid,  the  quinine  will 
become  quinine  sulphate,  and,  being  insoluble  in  the  chloroform,  will  then 
leave  that  solvent,  and  pass  to  the  aqueous  layer  once  more  in  its  original 
form.  The  main  exception  to  these  rules  is  morphine,  which  only  comes  out 
satisfactorily  from  its  alkalised  salts  to  warm  amylic  alcohol.  If  a  drug 
should  also  contain  resinous  or  other  matters  soluble  in  the  chloroform,  they 
will  come  into  it  with  the  free  alkaloids,  but  will  remain  behind  when  the 
chloroformic  solution  is  acted  upon  by  acidulated  water.  The  process  is  done 
in  a  separator  (see  fig.  17,  p.  93),  and  the  following  precautions  are  so  lucidly 
described  by  the  U.S. P.  that  they  cannot  be  improved  upon : — 

When  the  solution  of  an  alkaloid,  suitably  prepared,  is  introduced  into  a 
separator,  and  chloroform  subsequently  added,  the  latter,  owing  to  its  higher 
specific  gravity,  will  form  the  lower  layer.  If  the  two  layers  are  violently 
shaken  together,  there  will  often  result  an  emulsion,  which  will  separate  only 
slowly,  and  often  imperfectly.  This  is  particularly  liable  to  happen  when  the 
aqueous  liquid  containing  the  alkaloid  either  in  suspension  or  in  solution  is 
strongly  alkaline,  and  when  it  has  a  high  specific  gravity.  To  avoid  the 
formation  of  an  emulsion,  the  extraction  should  be  accomplished  rather  by 
rapid  rotation  and  frequent  inversion  of  the  separator  than  by  violent  shaking. 
When  an  emulsion  has  formed,  its  separation  may  be  promoted  by  the 
addition  of  more  of  the  solvent,  preferably  somewhat  heated,  aided,  if 
necessary,  by  the  external  application  of  a  gentle  heat  (the  stopper  being 
removed  for  the  time  being),  or  by  the  introduction  of  a  small  quantity  of 
alcohol  or  of  hot  water.  The  separation  of  the  two  layers  may  also  be 
promoted  by  stirring  the  lower,  chloroformic  layer  with  a  glass  rod,  and 
detaching  from  the  walls  of  the  separator  the. adhering  drops  of  emulsion. 
On  withdrawing  the  chloroform  solution  of  an  alkaloid  from  the  separator,  a 
small  amount  of  the  solution  will  generally  be  retained  in  the  outlet  tube  by 


U.S. P.   ASSAYS  OF  DRUGS.  18; 

capillary  attraction.  If  this  were  lost,  the  results  of  the  assay  would  be 
seriously  vitiated.  To  avoid  this  loss,  several  successive,  small  portions  of 
chloroform  should  be  poured  into  the  separator  without  agitation,  and  drawn 
off  through  the  stopcock  to  wash  out  the  outlet  tube.  Another  source  of 
loss  is  the  pressure  sometimes  generated  in  the  separator  by  the  rise  of 
temperature  caused  when  an  alkaline  and  an  acid  liquid  are  shaken  together. 
On  loosening  the  stopper,  the  liquid  which  adheres  to  the  juncture  of  the 
latter  with  the  neck  is  liable  to  be  ejected.  This  is  best  avoided  by  mixing 
the  liquids  at  first  by  rotation  (avoiding  contact  of  the  contents  with  the 
stopper),  and  allowing  them  to  become  cold  before  stoppering  the  separator. 
The  same  precautions  should  be  observed  when  an  alkali  carbonate  has  been 
used,  in  place  of  a  caustic  alkali,  for  setting  free  the  alkaloid.  In  this  case 
the  liquids  should  be  cautiously  and  gradually  mixed  by  rotation,  and  the 
separator  should  be  left  unstoppered  until  gas  is  no  longer  given  off.  If  a 
regular  glass  separator  is  not  available,  and  the  quantity  of  liquid  is  small,  an 
ordinary  burette,  stoppered  with  a  sound  cork,  may  be  employed  in  its  place. 

III.  U.S.P.  ASSAYS  OF  DRUGS  WHERE  THE  ALKALOIDAL  RESIDUE 

IS  WEIGHED. 

(1)  Alkaloidal  Scale  Preparations. 

(a)  Ferri  et  quinines  citrus.  Introduce  i'n  Gm.  of  iron  and  quinine  citrate 
in  a  dish,  and,  with  the  aid  of  a  gentle  heat,  dissolve  it  in  20  Cc.  of  water. 
Transfer  the  solution,  together  with  the  rinsings  of  the  dish,  to  a  separator, 
allow  the  liquid  to  become  cold,  then  add  5  Cc.  of  ammonia  water  and  10  Cc. 
of  chloroform,  and  shake  the  separator  for  one  minute.  Allow  the  liquids  to 
separate,  draw  off  the  chloroformic  layer,  and  shake  the  residuary  liquid  a 
second  and  a  third  time  with  portions  of  10  Cc.  each  of  chloroform.  Allow 
the  combined  chloroformic  solutions  to  evaporate  spontaneously  in  a  tared 
dish,  and  dry  the  residue  at  100°  C.  (212°  F.)  to  a  constant  weight.  This 
residue  should  weigh  not  less  than  0*1276  Gm.  (corresponding  to  at  least 
1 1 -5  per  cent,  of  dried  quinine).* 

(b}  Ferri  et  strychnines  citras.  Dissolve  4*44  Gm.  of  iron  and  strychnine 
citrate,  in  a  separator,  in  15  Cc.  of  water,  add  5  Cc.  of  ammonia  water  and 
jo  Cc.  of  chloroform,  and  shake  the  separator  for  one  minute.  Allow  the 
liquids  to  separate,  draw  off  the  chloroformic  layer,  and  shake  the  residuary 
liquid  a  second  and  a  third  time  with  portions  of  10  Cc.  each  of  chloroform. 
Allow  the  combined  chloroformic  liquids  to  evaporate  spontaneously  in  a 
tared  dish,  and  dry  the  residue  at  ico°  C.  (212°  F.)  to  a  constant  weight. 
This  residue  should  weigh  not  less  than  0*04  (0-0399)  Gm.  nor  more  than 
0-0444  Gm.  (corresponding  to  not  less  than  0*9  nor  more  than  i  per  cent,  of 
strychnine). 

(2)  Colchicum  and  its  Preparations. 

(a)  Assay  of  colchicum  corm.  Introduce  10  Gm.  of  colchicum  corm  (in 
No.  60  powder)  into  a  200  Cc.  Erlenmeyer  flask,  and  add  to  it  100  Cc.  of  a 
mixture  of  77  Cc.  of  ether,  25  Cc.  of  chloroform,  8  Cc.  of  alcohol,  and  3  Cc. 
of  ammonia  water,  insert  the  stopper  securely,  and  macerate,  with  frequent 
shaking,  for  twelve  hours  (or  preferably  for  four  hours  in  a  mechanical  shaker). 
Filter  off  50  Cc.  of  the  liquid  (representing  5  Gm.  of  colchicum  corm),  transfer 
this  to  a  beaker,  and  evaporate  it  nearly  to  dryness  at  a  gentle  heat.  Dissolve 
the  residue  in  10  Cc.  of  ether,  add  5  Cc.  of  water,  stir  well,  and  heat  gently 

*  The  U.S.P.  uses  the  aqueous  liquids  left  in  the  separator  after  extraction  of  the  alkaloids 
for  the  volumetric  estimation  of  the  iron  by  the  "  hypo  "  process  (see  p.  122). 


1 88  ANALYSIS  OF  DRUGS,   ETC. 

until  the  ether  has  evaporated.  After  cooling,  filter  the  aqueous  solution  inta 
a  small  separator,  retaining  the  insoluble  matter  as  much  as  possible  in  the 
beaker  or  dish.  Redissolve  the  residue  in  a  little  ether,  add  5  Cc.  of  water, 
and  proceed  as  before.  Wash  the  container  and  filter  with  a  little  water,  and 
shake  the  combined  aqueous  solutions  well  for  one  minute  with  15  Cc.  of 
chloroform.  Draw  off  the  chloroform,  after  separation,  into  a  beaker,  and 
again  shake  out  the  aqueous  liquid  successively  with  three  portions  of  10  Cc. 
each  of  chloroform,  collecting  these  solutions  in  the  beaker.  Evaporate  the 
chloroform  completely  ;  dissolve  the  residue  in  a  little  alcohol,  evaporate  the 
latter,  redissolve  the  residue  in  5  Cc.  of  ether,  add  5  Cc.  of  water,  and  stir 
the  liquid  for  a  few  seconds.  Then  evaporate  the  ether  on  a  water-bath  con- 
taining warm  water,  and  filter  the  remaining  aqueous  liquid  through  a  small 
wetted  filter  into  a  separator,  washing  the  dish  and  filter  with  5  Cc.  of  water, 
and  adding  the  washings  to  the  separator.  Shake  out  the  aqueous  liquid 
with  15  Cc.  of  chloroform,  and  draw  off  the  separated  chloroform  into  a  tared 
flask.  Repeat  the  shaking  out  successively  with  three  portions  of  10  Cc.  of 
chloroform  and  add  each  to  the  tared  flask.  Evaporate  the  chloroform, 
dissolve  the  residue  in  a  little  alcohol,  evaporate  the  latter,  redissolve  the 
residue  in  alcohol,  evaporate  the  alcohol  as  before,  and  dry  the  residue  at 
100°  C.  (212°  F.)  until  the  weight,  after  cooling,  remains  constant.  The 
weight  of  the  residue  multiplied  by  20  gives  the  percentage  of  colchicine  in 
the  colchicum  corm. 

(b)  Assay  of  extract  of  colchicum  corm.     Dissolve  4  Gm.  of  the  extract  of 
colchicum   corm    in    20    Cc.   of   distilled  water,    transfer   the   solution  to  a 
graduated  flask,  and  add  sufficient  alcohol  to  make  the  liquid  measure  100  Cc. 
Shake  the  flask  well,  allow  it  to  stand  for  five  minutes,  filter,  and  collect  50  Cc. 
of  the  filtrate  (representing  2  Gm.  of  the  extract),  and  evaporate  it  to  dryness 
in  a  porcelain  dish  by  means  of  a  water- bath.     Add  to  the  residue  10  Cc.  of 
ether  and  5  Cc.  of  distilled  water,  stir  the  mixture  well  and  heat  it  gently 
until  the  ether  is  evaporated.     After  cooling,  pour  off  the  aqueous  solution, 
filtering  it  into  a  separator,  retaining  as  much  of  the  insoluble  matter  in  the 
dish  as  possible.     Again  treat  the  residue  with  10  Cc.  of  ether,  and  5  Cc.  of 
water,  and  proceed  as  before ;  rinse  the  dish  and  filter  with  a  little  water  and 
collect  all  of  the  aqueous  liquids  in  the  separator.     Introduce  a  small  piece  of 
red  litmus  paper  into  the  separator,  add  enough  ammonia  water  to  render  the 
liquid  alkaline,  and  then  shake  it  out  with  three  successive  portions  of  chloro- 
form, of  20,  15,  and  10  Cc.  respectively.     Collect  the  combined  chloroformic 
solutions  in  an  Erlenmeyer  flask,  evaporate  the  chloroform,  and  add  to  the 
alkaloidal  residue  two  successive  small  portions  of  alcohol,  evaporating  the 
alcohol  each  time.     Now  add'  to  the  residue  a  mixture  of  5  Cc.  of  distilled 
water  and  10  Cc.  of  ether,  agitate  the  liquid  gently  and  evaporate  the  ether  ; 
after  cooling  filter  the  aqueous  liquid  into  a  separator.     Rinse  the  flask  with 
distilled  water,  pass  the  rinsings  through   the  filter  into  the  separator,  and 
shake  out  the  aqueous  solutions  with  three  successive  portions  of  chloroform, 
20,  15,  and  10  Cc.  respectively.     Collect  the  combined  chloroformic  solutions 
in  a  tared  Erlenmeyer  flask,  evaporate  the  chloroform,  and  treat  the  alkaloidal 
residue  with  two  successive  small  portions  of  alcohol,  evaporating  the  alcohol 
each  time,  and  dry  the  residue,  at  100°  C.  (212°  F.),  to  a  constant  weight. 
The  weight  multiplied  by  50  will  give  the  percentage  of  colchicine  in  the 
extract  of  colchicum  conn. 

(c)  Assay  of  colchicum  seed.     Introduce  10  Gm.  of  colchicum  seed  into  a 
200  Cc.  Erlenmeyer  flask,  and  add  to  it   100  Cc.  of  a  mixture  of  77  Cc.  of 
ether,  25  Cc.  of  chloroform,  8  Cc.  of  alcohol,  and  3  Cc.  of  ammonia  water,  insert 
the  stopper  securely,  and  macerate,  with  frequent  shaking,  for  twelve  hours 
(or  preferably  for  four  hours  in  a  mechanical  shaker).     Filter  the  liquid  into  a 


U.S.P.   ASSAYS  OF  DRUGS.  189 

measuring  cylinder  until  50  Cc.  of  filtrate  (representing  5  Gm.  of  colchicum 
-seed)  have  been  obtained;  then  transfer  this  to  a  beaker  or  dish,  and 
evaporate  it  nearly  to  dryness  by  applying  a  very  gentle  heat.  Dissolve  the 
residue  in  10  Cc.  of  ether,  add  5  Cc.  of  water,  stir  well,  and  heat  gently  until 
the  ether  has  evaporated.  After  cooling  filter  the  aqueous  solution  into  a 
small  separator,  retaining  the  insoluble  matter  as  much  as  possible  in  the 
beaker  or  dish.  Redissolve  the  residue  in  a  little  ether,  add  5  Cc.  of  water, 
and  proceed  as  before.  Wash  the  container  and  filter  with  a  little  water,  and 
shake  the  combined  aqueous  solutions  well  for  one  minute  with  15  Cc.  of 
chloroform.  Draw  off  the  separated  chloroform  into  a  tared  flask,  and  again 
shake  out  the  aqueous  liquid  successively  with  three  portions  of  10  Cc.  each 
•of  chloroform,  collecting  these  solutions  in  the  tared  flask.  Evaporate  the 
chloroform  ;  dissolve  the  residue  in  a  little  alcohol,  evaporate  the  latter, 
redissolve  the  residue  in  alcohol,  evaporate  the  alcohol  as  before,  and  dry  the 
residue  at  100°  C.  (212°  F.)  until  the  weight,  after  cooling,  remains  constant. 
The  weight  of  the  residue  multiplied  by  20  gives  the  percentage  of  colchicine 
in  the  colchicum  seed. 

(d)  Assay  of  fluidextract  of  colchicum  seed.     Measure  into  a  separator  10  Cc. 
of  fluidextract  of  colchicum  seed,  add  i  Cc.  of  ammonia  water,  and  shake  out 
the  alkaloid  with  three  successive  portions,  15,  15,  and  10  Cc.,  of  chloroform. 
Collect  the  chloroformic  solution  in  a  beaker  or  dish,  and  evaporate  it  nearly 
to  dryness  by  applying  a  very  gentle  heat.     Dissolve  the  residue  in  10  Cc.  of 
ether,  add  5  Cc.  of  water,  stir  well,  and  heat  gently  until  the  ether  is  evaporated. 
From  this  point  the  process  goes  on  as  for  colchicum  seed,  and  the  weighed 
residue  so  obtained  is  multiplied  by  10,  which  gives  Cms.  of  colchicine  in 
100  Cc.  of  the  extract  analyzed. 

(e)  Assay  of  tincture  of  colchicum  seed.     Transfer   TOO   Cc.  of   tincture  of 
colchicum  seed  to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until 
it  measures  about  10  Cc.     Add,  if  necessary,  sufficient  alcohol  to  dissolve  any 
separated  substance,  and  then  assay  the  resulting  liquid  by  the  method  above 
given  for  the  fluidextract,  with  the  exception  that  the  multiplication  of  the 
product  by  10  be  omitted;  the  result  will  represent  the  weight  in  Gms.  of 
colchicine  contained  in  one  hundred  cubic  centimeters  of  tincture  of  colchicum 
seed. 

(3)  Conium  and  its  Preparations. 

(a)  Assay  of  conium.  Place  10  Gm.  of  conium  in  a  200  Cc.  Erlenmeyer 
flask,  add  100  Cc.  of  a  mixture  of  ether  98  parts,  alcohol  8  parts,  and 
ammonia  water  3  parts  (by  volume),  insert  the  stopper  securely,  and  shake 
the  flask  at  intervals  during  four  hours.  After  the  powder  has  settled,  decant 
50  Cc.  of  the  clear  liquid  into  a  beaker  (representing  5  Gm.  of  conium),  and 
add  sufficient  N.  H2SO4  to  produce  a  distinctly  acid  reaction.  Evaporate  the 
ether  at  a  gentle  heat  by  the  aid  of  a  water-bath ;  then  add  15  Cc.  of  alcohol, 
and  set  the  beaker  aside  in  a  cool  place  for  two  hours  to  allow  the  ammonium 
sulphate  to  deposit.  Filter;  wash  the  residue  and  filter  with  a  little  alcohol, 
and  add  the  washings  to  the  filtrate ;  neutralize  any  excessive  amount  of  acid 
with  sodium  carbonate,  being  careful  to  retain  a  slight  acidity.  Concentrate 
the  liquid  to  3  Cc.  by  the  aid  of  a  gentle  heat  on  a  water-bath,  add  3  Cc.  of 
distilled  water  and  2  drops  of  N.  H2SO4.  Add  15  Cc.  of  ether  to  remove 
traces  of  fatty  matter,  pour  off  the  ether-solution  and  repeat  the  washing  with 
15  Cc.  of  ether.  Then  transfer  the  acid  liquid  to  a  separator,  introduce  a 
small  piece  of  red  litmus  paper,  and  add  sufficient  sodium  carbonate  to 
render  the  liquid  slightly  alkaline ;  then  shake  out  with  successive  portions 
°f  T5>  J5»  an<3  I0  Cc.  °f  ether.  To  the  combined  ether-solutions,  in  a  tared 


1 9o  ANALYSIS  OF  DRUGS,  ETC. 

beaker,  add,  drop  by  drop,  sufficient  hydrochloric  acid  solution  (5  per  cent.) 
to  insure  an  excess  of  acid,  and  then  evaporate  the  ether  by  a  gentle  heat  on 
a  water-bath.  Remove  the  excess  of  hydrochloric  acid  by  adding  to  the 
residue  3  Cc.  of  alcohol  and  heating  gently  to  evaporate  the  liquid ;  repeat 
this  operation  once,  and  dry  the  residue  at  a  temperature  not  exceeding 
60°  C.  (140°  F.)  until  the  weight,  after  cooling  in  a  desiccator,  remains 
constant.  The  weight  of  the  residue  multiplied  by  0*777,  and  this  product 
by  20,  gives  the  percentage  of  coniine  contained  in  the  conium. 

(b)  Assay  of  fluidextract  of  conium.  Transfer  10  Cc.  of  fluidextract  of 
conium  by  means  of  a  graduated  pipette  to  an  evaporating  dish  containing  a 
little  clean  sand,  and  evaporate  it  to  dryness  at  a  gentle  heat.  Mix  the  sand 
uniformly  with  the  extract  and  transfer  it  to  an  Erlcnmeyer  flask  of  about 
200  Cc.  capacity,  rinse  the  dish  with  100  Cc.  of  a  mixture  of  ether  100  Cc., 
alcohol  7  Cc.,  and  ammonia  water  3  Cc.,  added  in  portions,  and  transfer  the 
rinsings  to  the  flask.  Insert  the  stopper  securely  and  shake  the  flask  at 
intervals  during  one  hour.  Decant  50  Cc.  of  the  liquid  (representing  5  Cc. 
of  the  fluidextract  of  conium)  into  a  beaker,  and  add  sufficient  N.  H2SO4  to 
produce  a  distinctly  acid  reaction.  Evaporate  the  ether  at  a  gentle  heat  by 
the  aid  of  a  water-bath;  then  add  15  Cc.  of  absolute  alcohol,  and  set  the 
beaker  aside  in  a  cool  place  for  two  hours  to  allow  the  ammonium  sulphate 
to  deposit.  Filter  the  liquid  and  proceed  as  above  directed  for  the  assay  of 
conium.  The  weighed  residue  multiplied  by  0777  x  20  =  Cms.  of  coniine 
in  100  Cc.  of  fluidextract. 

(4)  Cinchona  and  its  Preparations. 

(a)  Assay  of  cinchona.  Introduce  15  Gm.  of  cinchona  (in  No.  80  powder 
or  finer)  into  an  Erlenmeyer  flask  or  bottle  of  about  200  Cc.  capacity,  and  add 
a  mixture  of  125  Cc.  of  ether  and  25  Cc.  of  chloroform;  then  insert  the 
stopper  securely,  shake  vigorously,  and  set  aside  for  ten  minutes.  Then  add 
10  Cc.  of  ammonia  water,  and  set  aside  for  five  hours,  shaking  at  frequent 
intervals  (or  continuously  with  the  aid  of  a  mechanical  shaker).  Next  add 
15  Cc.  of  distilled  water,  shake  vigorously,  and  allow  it  to  stand  for  a  few 
minutes,  to  cause  the  powder  to  settle.  Measure  off  100  Cc.  of  the  clear 
supernatant  fluid  (representing  10  Gm.  of  cinchona),  transfer  this  to  a  separator 
and  add  15  Cc.  of  N.  H2SO4  or  sufficient  to  make  the  liquid  distinctly  acid. 
Shake  the  separator  vigorously  for  one  minute,  and  allow  the  two  layers  of 
liquid  to  separate  completely.  Draw  off  the  lower  aqueous  layer  into  the 
flask.  Then  add  5  Cc.  of  N.  H2SO4  and  5  Cc.  of  distilled  water  to  the 
separator  and  shake  it  vigorously  for  about  one  minute,  allow  the  liquids  to 
separate  as  before,  and  again  draw  off  the  lower  aqueous  layer  into  the  flask. 
Repeat  the  operation,  using  5  Cc.  of  distilled  water  in  the  separator  (without 
acid),  drawing  off  the  aqueous  liquid  into  the  flask.  Filter  the  combined  acid 
liquids  into  a  measuring  cylinder,  and  wash  the  filter  and  flask  with  enough 
distilled  water  to  make  the  contents  of  the  cylinder  measure  exactly  50  Cc. 
Pour  half  (25  Cc.)  of  the  acid  liquid  into  a  separator  marked  No.  i,  and  the 
remaining  half  (25  Cc.)  into  another  separator  marked  No.  2,  which  set  aside. 

i.  for  anhydrous  cinchona  alkaloids.  To  separator  No.  i  (see  above)  add 
25  Cc.  of  a  mixture  of  chloroform  3  volumes  and  ether  i  volume,  also  5  Cc. 
of  ammonia  water,  or  sufficient  to  render  the  liquid  alkaline.  Insert  the 
stopper,  shake  for  one  minute,  and  then  draw  off  the  lower  layer  into  a  tared 
flask.  Add  20  Cc.  more  of  the  chloroform-ether  mixture  to  the  separator, 
insert  the  stopper,  and  shake  for  one  minute,  again  drawing  off  the  lower  layer 
into  the  tared  flask.  Repeat  the  operation  with  10  Cc.  of  chloroform,  and 
draw  this  off  into  the  tared  flask.  Evaporate  the  chloroform-ether  solutions 


U.S.P.  ASSAYS  OF  DRUGS.  191 

in  the  tared  flask  slowly  and  carefully  to  dryness  on  a  water-bath.  Add  3  Cc. 
of  ether  to  the  dry  residue,  and  again  evaporate  to  dryness.  Then  place  the 
flask  in  an  air-bath  and  heat  at  110°  C.  (230°  F.)  until  the  weight  after  cooling 
remains  constant.  This  weight  in  Gms.  multiplied  by  20  will  give  the  per- 
centage of  anhydrous  cinchona  alkaloids  (total  alkaloids)  in  the  cinchona. 

2.  For  ether-soluble  alkaloids.  To  separator  No.  2  (see  above),  containing 
the  other  25  Cc.  of  acid  liquid,  add  25  Cc.  of  ether  and  5  Cc.  of  ammonia 
water,  or  sufficient  to  render  the  liquid  alkaline.  The  temperature  of  the 
liquid  should  be  kept  below  20°  C.  (68°  F.),  by  cooling  it,  if  necessary.  Shake 
the  separator  moderately  for  two  minutes,  and  allow  the  liquid  to  stand  for 
ten  minutes  at  15°  C.  (59°  F.) ;  after  the  liquids  have  separated,  draw  off  and 
reject  the  lower  aqueous  layer  and  transfer  the  ethereal  liquid  to  a  tared 
beaker.  Add  5  Cc.  more  of  ether  to  the  separator,  rinse  carefully,  and  add 
the  rinsings  to  the  tared  beaker.  Evaporate  the  ether  carefully  by  the  aid  of 
a  water-bath,  dry  the  beaker  and  contents  in  an  air-bath  at  110°  C.  (230°  F.) 
for  two  hours,  cool,  and  weigh.  This  weight  in  Gms.  multiplied  by  20  gives 
the  percentage  of  the  anhydrous  ether-soluble  alkaloids  contained  in  the 
cinchona. 

Note. — Ether-soluble  alkaloids  include  quinine,  quinidine,  and  cinchonidine. 

(&)  Assay  of  fluidextract  of  cinchona.  Transfer  10  Cc.  of  fluidextract  of 
cinchona  by  means  of  a  graduated  pipette  to  an  Erlenmeyer  flask  of  200  Cc. 
capacity,  and  add  a  mixture  of  100  Cc.  of  ether,  25  Cc.  of  chloroform,  and 
10  Cc.  of  ammonia  water.  Insert  the  stopper,  and  shake  the  flask,  at  intervals, 
during  10  minutes.  Allow  the  liquids  to  separate,  decant  exactly  66  Cc.  of 
the  supernatant  liquid  (representing  5  Cc.  of  the  fluidextract),  and  transfer  this 
to  a  separator,  rinsing  the  measure  with  5  Cc.  of  ether  and  adding  this  to  the 
separator.  Add  to  the  latter  about  10  Cc.  of  N.  H2SO4,  or  enough  to  make 
the  solution  distinctly  acid,  and  shake  the  separator  vigorously  for  several 
minutes,  and  when  the  liquids  have  completely  separated,  draw  off  the  lower 
layer  into  a  second  separator.  To  the  first  separator  add  5  Cc.  more  of 
N.  H2SO4,  and  5  Cc.  of  distilled  water,  shake  it  for  several  minutes,  and  when 
the  liquids  have  separated,  draw  off  the  lower  layer  into  the  second  separator. 
Now  add  5  Cc.  of  distilled  water  to  the  first  separator,  shake  it,  separate  as 
before,  and  then  draw  off  the  lower  aqueous  layer  into  the  second  separator. 
To  the  second  separator  add  25  Cc.  of  ether,  a  small  piece  of  red  litmus  paper, 
and  then,  gradually,  ammonia  water,  keeping  the  temperature  of  the  liquids 
below  25°  C.  (77°  F.),  until  the  reaction  is  alkaline.  Then  shake  the  separator 
for  two  minutes,  and  allow  the  liquids  to  stand  for  ten  minutes  at  a  tempera- 
ture below  15°  C.  (59°  F.).  Draw  off  and  reject  the  lower  aqueous  layer,  and 
then  transfer  the  ether-layer  into  a  tared  beaker.  Add  5  Cc.  more  of  ether 
to  the  separator,  rinse  carefully,  and  add  the  rinsings  to  the  tared  beaker, 
and  entirely  evaporate  the  ether  at  a  moderate  heat  on  a  water-bath.  Then 
dry  the  beaker  in  an  air-bath  at  120°  C.  (248°  F.)  for  half  an  hour,  cool,  and 
weigh.  Replace  the  beaker  in  the  air-bath,  and  heat  again  at  the  same 
temperature  for  half  an  hour,  cool,  and  weigh,  repeating  until  the  weight  is 
constant.  Multiply  the  weight  of  the  residue  by  20  to  obtain  the  weight  in 
Gms.  of  anhydrous  ether-soluble  alkaloids  contained  in  100  Cc.  of  the  fluid- 
extract  of  cinchona. 

(c)  Assay  of  tincture  of  cinchona.  Transfer  50  Cc.  of  tincture  of  cinchona 
to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  it  measures 
about  10  Cc.,  transfer  the  liquid  to  a  bottle  having  the  capacity  of  about 
1 80  Cc.,  rinsing  the  dish  with  10  Cc.  of  diluted  alcohol,  then  assay  the 
resulting  liquid  by  the  method  above  given  for  the  fluidextract,  with  the 
exception  that  the  multiplication  of  the  product  should  be  by  4  instead  of  20 ; 


i92  ANALYSIS   OF  DRUGS,   ETC. 

the  result  will  represent  the  weight  in  Gms.  of  anhydrous  ether-soluble  alka- 
loids contained  in  one  hundred  cubic  centimeters  of  tincture  of  cinchona. 

(5)  Guarana  and  its  Preparations. 

(a)  Assay  of  gnat-ana.  Introduce  6  Gm.  of  guarana  (in  No.  60  powder) 
into  an  Erlenmeyer  flask,  and  pour  upon  it  120  Cc.  of  chloroform  and  6  Cc. 
of  ammonia  water,  and  insert  the  stopper  securely.  Shake  the  flask  at 
intervals  of  half  an  hour,  and  allow  it  to  stand  for  four  hours.  Filter  off 
100  Cc.  of  the  liquid  (representing  5  Gm.  of  guarana),  then  transfer  the 
filtrate  to  a  flask,  and  distil  off  all  of  the  chloroform  by  means  of  a  water-bath. 
Dissolve  the  alkaloid.il  residue  in  a  mixture  of  2  Cc.  of  N.  H2SO4  and  20  Cc. 
of  warm  distilled  water.  Allow  the  liquid  to  cool,  and  filter  it  into  a 
separator,  rinse  the  flask  and  filter  with  several  small  portions  of  distilled 
water,  add  20  Cc.  of  chloroform  and  2  Cc.  of  ammonia  water  to  the  separator, 
and  shake  it  for  one  minute.  Draw  off  the  chloroform  into  a  tared  flask  and 
repeat  the  extraction  with  two  portions  of  10  Cc.  each  of  chloroform.  Distil 
off  the  chloroform  from  the  combined  liquids,  and  when  the  residue  is  dry, 
add  2  Cc.  of  ether  and  evaporate  on  a  water-bath  very  carefully  to  avoid 
decrepitation ;  continue  the  heating  until  the  weight  of  the  residue  after 
cooling  remains  constant.  This  weight  multiplied  by  20  will  give  the  per- 
centage of  the  alkaloidal  principles  contained  in  the  guarana, 

(/>)  Assay  of  flnidextract  of  guarana.  Transfer  to  a  separator  5  Cc.  of 
fluidextract  of  guarana,  add  15  Cc.  of  chloroform  and  i  Cc.  of  ammonia 
water.  Shake  well  and  allow  the  liquid  to  separate  completely.  Draw  oft' 
the  chloroform  into  a  beaker.  Shake  out  the  fluid  remaining  in  the  separator 
with  two  additional  portions  of  chloroform  of  10  Cc.  each ;  evaporate  the 
combined  chloroformic  solutions  carefully  to  dry  ness.  From  this  point 
proceed  as  above  given  for  the  assay  of  guarana,  when  the  result  will  be  the 
weight  in  Gms.  of  alkaloids  in  100  Cc.  of  the  fluidextract. 

(6)  Hydrastis  and  its  Preparations. 

(a)  Assay  oj  hydrastis.  Introduce  15  Gm.  of  hydrastis  (in  No.  60  powder) 
into  an  Erlenmeyer  flask  of  250  Cc.  capacity,  add  150  Cc.  of  ether,  shake  the 
flask  during  ten  minutes,  and  add  5  Cc.  of  ammonia  water,  again  shaking  the 
flask  at  intervals  during  half  an  hour.  Then  add  15  Cc.  of  distilled  water  to 
the  mixture  in  the  flask  and  shake  it  until  the  drug  collects  in  masses,  and  at 
once  pour  off  100  Cc.  of  the  supernatant  ether-solution  and  transfer  it  to  a 
separator.  Add  15  Cc.  of  N.  H2SO4  to  the  separator,  and  shake  during 
one  minute.  Allow  the  liquids  to  separate,  and  draw  off  the  lower  acid  liquid 
into  a  second  separator.  Again  shake  out  the  ether-solution  with  5  Cc.  of 
N.  H2SO4  and  5  Cc.  of  distilled  water,  and  shake  for  one  minute.  After 
separation,  draw  off  the  acid  solution  as  before  into  the  second  separator. 
Repeat  process  with  5  Cc.  of  distilled  water,  drawing  this  also  into  the  second 
separator.  Introduce  a  small  piece  of  red  litmus  paper  into  the  second  sepa- 
rator, add  enough  ammonia  water  to  render  the  liquid  alkaline,  and  then  25  Cc. 
of  ether,  and  shake  the  separator  during  one  minute,  and  when  the  liquids  have 
separated  draw  off  the  lower  alkaline  liquid  into  another  separator,  and  the 
ether-solution  into  a  tared  beaker.  Again  shake  out  the  alkaline  liquid,  using 
20  Cc.  of  ether,  shake  the  separator  for  one  minute,  and,  after  separation, 
draw  off  the  alkaline  liquid  into  the  other  separator,  and  the  ether-solution 
into  the  tared  beaker.  Finally,  again  shake  out  the  alkaline  liquid,  using 
15  Cc.  of  ether,  proceeding  as  before,  and  adding  the  ether-solution  to  the 
liquid  in  the  tared  beaker.  Evaporate  the  ether  carefully  with  the  aid  of  a 
water-bath,  and  dry  the  alkaloidal  residue  in  the  beaker  to  a  constant  weight 


U.S.P.   ASSAYS   OF  DRUGS.  193 

at   100°  C.  (212°  K).     The  weight  found,  multiplied  by  10,  will  give  the 
percentage  of  hydrastine  in  the  hydrastis. 

(b)  Assay  of  fluidextract  of  hydrastis.  Transfer  10  Cc.  of  fluidextract  of 
hydrastis  by  means  of  a  graduated  pipette  to  a  100  Cc.  measuring  flask,  add 
85  Cc.  of  distilled  water  in  which  2  Gm.  of  potassium  iodide  have  been 
previously  dissolved,  and  sufficient  water  to  make  100  Cc.,  and  shake  the 
liquid  for  several  minutes.  Then  filter  off  50  Cc.  of  the  liquid  and  transfer 
it  to  a  separator.  Render  the  liquid  alkaline  with  ammonia  water,  add  30  Cc. 
of  ether,  and  shake  the  separator  at  intervals  during  several  minutes.  When 
separated,  draw  off  the  aqueous  layer  into  a  beaker,  and  the  ether-solution 
into  a  tared  beaker.  Return  the  aqueous  solution  to  the  separator,  and  shake 
it  with  20  Cc.  more  of  ether  for  one  minute.  Draw  off  and  reject  the  aqueous 
layer,  and  run  the  ether-solution  into  the  tared  beaker.  Allow  the  combined 
ether-solutions  to  evaporate  at  a  gentle  heat,  and  dry  the  residue  in  the 
beaker  to  a  constant  weight  on  a  water-bath.  Multiply  the  weight  by  20, 
which  will  give  the  weight  in  Gms.  of  hydrastine  contained  in  one  hundred 
cubic  centimeters  of  fluidextract  of  hydrastis. 

(f)  Assay  of  tincture  of  hydrastis.  Transfer  100  Cc.  of  tincture  of  hydrastis 
to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  the  liquid 
measures  about  10  Cc.  If  any  insoluble  matter  has  separated,  add  sufficient 
alcohol  to  dissolve  it,  and  then  assay  the  resulting  liquid  by  the  method 
given  above  for  the  fluidextract,  with  the  exception  that  the  weight  of  the 
residual  alkaloids  must  be  multiplied  by  2  instead  of  by  20  as  there  directed, 
to  give  the  weight  in  Gms.  of  hydrastine  contained  in  one  hundred  cubic 
centimeters  of  tincture  of  hydrastis. 

(7)  Opium  and  its  Preparations. 

(a)  Assay  of  opiiim.  Introduce  10  Gm.  of  opium  (which,  if  fresh, 
should  be  in  very  small  pieces,  and  if  dry,  in  very  fine  powder)  into  an 
Erlenmeyer  flask  having  a  capacity  of  about  300  Cc.,  add  100  Cc.  of  distilled 
water,  stopper  the  flask,  and  agitate  it  every  ten  minutes  (or  continuously 
in  a  mechanical  shaker)  during  three  hours.  Then  pour  the  contents  as 
evenly  as  possible  upon  a  wetted  filter  having  a  diameter  of  12  Cm.,  and, 
when  the  liquid  has  drained  off,  wash  the  residue  with  distilled  water,  dropped 
upon  the  edges  of  the  filter  and  its  contents,  until  150  Cc.  of  filtrate  have 
been  obtained.  Then  transfer  the  moist  opium  back  to  the  flask,  add  50  Cc. 
of  distilled  water,  agitate  it  thoroughly  during  fifteen  minutes,  and  return  the 
whole  to  the  filter.  When  the  liquid  has  drained  off,  wash  the  residue,  as 
before,  until  the  second  filtrate  measures  150  Cc.,  and  finally  collect  about 
20  Cc.  more  of  a  third  filtrate.  Evaporate  carefully  in  a  tared  dish,  first,  the 
second  filtrate  to  a  small  volume,  then  add  the  first  filtrate,  rinsing  the  vessels 
with  the  third  filtrate,  and  continue  the  evaporation  until  the  residue  weighs 
14  Gm.  Rotate  the  concentrated  solution  about  in  the  dish  until  the  rings 
of  extract  are  redissolved,  pour  the  liquid  into  a  tared  Elenmeyer  flask  having 
a  capacity  of  about  100  Cc.,  and  rinse  the  dish  with  a  few  drops  of  water  at 
a  time,  until  the  entire  solution,  after  the  rinsings  have  been  added  to  the 
flask,  weighs  20  Gm.  Then  add  10  Gm.  (or  12-2  Cc.)  of  alcohol,  shake  the 
flask  well,  add  25  Cc.  of  ether,  and  repeat  the  shaking.  Now  3*5  Cc. 
ammonia  water  (10  per  cent,  strength),  stopper  the  flask  with  a  sound  cork, 
shake  it  thoroughly  during  ten  minutes,  and  then  set  it  aside,  in  a  moderately 
cool  place,  for  at  least  six  hours,  or  over  night. 

Remove  the  stopper  carefully,  and  should  any  crystals  adhere  to  it,  brush 
them  into  the  flask.  Place  in  a  small  funnel  two  rapidly  acting  filters,  of  a 
diameter  of  7  Cm.,  plainly  folded,  one  within  the  other  (the  triple  fold  of  the 

13 


i94  ANALYSIS  OF  DRUGS,   ETC. 

inner  filter  being  laid  against  the  single  side  of  the  outer  filter),  wet  them  well 
with  ether,  and  derant  the  ethereal  solution  as  completely  as  possible  upon  the 
inner  filter.  Add  10  Cc.  of  ether  to  the  contents  of  the  flask,  rotate  it,  and 
again  decant  the  ethereal  layer  upon  the  inner  filter.  Repeat  this  operation 
with  another  portion  of  10  Cc.  of  ether.  Then  pour  the  liquid  in  the  flask 
into  the  filter,  in  portions,  in  such  a  way  as  to  transfer  the  greater  portion  of 
the  crystals  to  the  filter,  and,  when  the  liquid  has  passed  through,  transfer  the 
remaining  crystals  to  the  filter  by  washing  the  flask  with  several  portions  of 
water,  using  not  more  than  15  Cc.  in  all.  Use  a  feather  or  rubber-tipped 
glass  rod  to  remove  the  crystals  that  adhere  to  the  flask.  Allow  the  double 
filter  to  drain,  then  apply  water  to  the  crystals,  drop  by  drop,  until  they  are 
practically  free  from  mother-liquor,  and  afterwards  wash  them  drop  by  drop, 
from  a  pipette,  with  alcohol  previously  saturated  with  powdered  morphine. 
When  this  has  passed  through,  displace  the  remaining  alcohol  by  ether,  using 
about  10  Cc.  or  more,  if  necessary.  Allow  the  filter  to  dry  in  a  moderately 
warm  place,  at  a  temperature  not  exceeding  60°  C.  (140°  F.)  until  its  weight 
remains  constant,  then  carefully  transfer  the  crystals  to  a  tared  watch-glass 
and  weigh  them. 

Place  the  crystals  (which  are  not  quite  pure)  in  an  Elenmeyer  flask,  add 
lime  water  (10  Cc.  for  each  o'i  Gm.  of  morphine)  and  shake  the  flask  at 
intervals  during  half  an  hour.  Pass  the  liquid  through  two  counterpoised 
rapidly  acting,  plainly  folded  filters,  one  within  the  other  (the  triple  fold  of  the 
inner  filter  being  laid  against  the  single  fold  of  the  outer  filter),  rinse  the  flask 
with  more  lime  water  and  pass  the  washings  through  the  filter  until  the  filtrate, 
after  acidulating,  no  longer  yields  a  precipitate  with  mercuric  potassium 
iodide.  Press  the  filters  until  nearly  dry  between  bibulous  paper  and  dry 
them  to  a  constant  weight,  then  weigh  the  contents,  using  the  outer  filter  as  a 
counterpoise.  Deduct  the  weight  of  the  insoluble  matter  on  the  filter  from 
the  weight  of  the  impure  morphine  previously  found.  The  difference, 
multiplied  by  10,  represents  the  percentage  of  crystallized  morphine  contained 
in  the  opium. 

(b)  Assay  of  extract  of  opium.     Dissolve  4  Gm.   of  extract  of  opium   in 
30  Cc.  of  water,  filter  the  solution  through  a  small  filter,  and  wash  the  filter 
and  residue  with  water,  until  all  soluble  matters  are  extracted,  collecting  the 
*,vashings  separately.     Evaporate,  in  a  tared  dish,  on  a  water-bath,  first,  the 
washings  to  a  small  volume,  then  add  the  first  filtrate,  and  evaporate  the  whole 
to  a  weight  of  10  Gm. 

Determine  the  morphine  in  this  extract  by  the  method  above  given  for 
opium  (beginning  with  the  word  "  Rotate  "),  but  use  2*2  Cc.  of  ammonia  water 
instead  of  3*5  Cc.,  and  finally  multiply  by  25  instead  of  by  ic. 

(c)  Assay  of  tincture  of  opium.     Transfer  100  Cc.  of  tincture   of  opium   to 
an  evaporating  dish  and  evaporate  it  on   a  water-bath  to  about  20  Cc.,  add 
40  Cc.   of  water,  mix  thoroughly  and  set   the    liquid   aside    for   one  hour, 
occasionally  stirring  to  disintegrate  the  resinous  flakes  adhering  to  the  dish. 
Then  filter  the  liquid  and  wash  the  filter  and  residue  with  water,  until  all 
soluble  matter  is  extracted   (indicated  by  an  almost  colorless  filtrate),  and 
collect  the  washings  separately.     First  evaporate  the  washings  in  a  tared  dish, 
to  a  small  volume,  then  add  the   first  filtrate  and  evaporate  the  whole   to  a 
weight  of  14  Gm. 

Determine  the  morphine  in  this  extract  by  the  method  given  under  opium 
assay  (l>eginning  with  the  word  "  Rotate  "),  using  the  same  details  as  there 
directed  for  10  Gm.  of  opium,  with  the  exception  that  the  final  multiplication 
by  10  be  omitted.  The  result  will  represent  the  weight  in  Cms.  of 
crystallized  morphine  yielded  by  one  hundred  cubic  centimeters  of  tincture  of 
opium. 


TITRATION  OF  ALKALOIDAL   RESIDUES.  195 


IV.    TITRATION   OF   ALKALOIDAL   RESIDUES. 

When,  by  the  evaporation  of  the  immiscible  solvent  containing  it,  we  can 
obtain  the  alkaloid  in  a  sufficient  state  of  purity,  it  may  be  directly  weighed, 
but  in  most  cases  it  is  more  convenient  to  be  satisfied  with  a  residue  not 
absolutely  pure  and  to  ascertain  the  amount  of  real  alkaloid  contained  therein 
by  volumetric  analysis.  Alkaloids  behave  towards  acids  in  a  similar  manner 
to  ammonia,  which  we  have  already  seen  (Chap.  VII.)  to  be  best  estimated 
by  residual  titration — i.e.  by  first  adding  excess  of  standard  acid  and  then 
titrating  back  with.standard  alkali  to  ascertain  the  amount  of  acid  remaining 
uncombined  with  the  alkaloid,  and  thus  obtaining  the  amount  of  the  alkaloid 
by  difference.  The  standard  acid  is  usually  employed  of  ^  strength,  and  the 
alkali  of  ^.  The  following  table  shows  the  equivalent  amount  of  alkaloid  in 
Gms.  for  each  Cc.  of  ~^  acid  :— 

Alkaloid.  i  Cc.  ^  acid  =  i  Cc.  -^  acid  = 

Aconitine,  C3IH47NOU 0-06406  .  .  0-012811 

Atropine,  C,7H.,3NO3 0-02870  .  .  0*005741 

Brucine,  C.aH.>(jN.,O4 0*03913  .  .  0*007826 

Cephaeline,  C,"4H,9NO2 0*02314  .  .  0-004628 

Cinchonicline,  C,9H22N2O  ....  0*02920  .  .  0*005841 

Cinchonine,  C19H2,N2O  .  .  .  .  0^02920  .  .  0*005841 

Combined  alkaloids  of  cinchona  .  .  .  0-03069  .  .  O '006139 

,,  ,,  of  ipecac.  .  .  .  0-02384  .  .  0*004768 

Cocaine,  C|7H21NO4 0*03009  .  .  0*006018 

Coniine,  C8H,7N  ......  0-01262  .  0*002524 

Emetine,  C15H,,NO2 0*02453  .  .  0*004906 

Hydrastine,  C2JH21NO8 0*03803  .  .  0-007606 

Morphine,  crystallized,  C17H19NO3  +  H2O  .  0*03009  .  .  O'oo6oi8 

„  anhydrous,  C,7H19NO3  .  .  .  0*02830  .  .  0*005661 

Physostigmine,  C15H21N3O2  ....  0*02732  .  .  0*005464 

Pilocarpine,  CUHJ6N2O2  .  0*02066  .  .  0*004133 

Quinine,  C.0H24N2O2  " 0*03218  .  .  0*006436 

Strychnine,"  C2IH22NvO2 0-03317  .  .  0*006635 

It  is  manifest  that  each  Cc.  of  f$  alkali  would  also  correspond  to  the  same 
amount  of  alkaloid  as  i  Cc.  of  ^j  acid.  The  indicators  employed  in  these 
titrations  are  : — 

(a)  Cochineal.     Macerate  i   Gm.  of  unbroken  cochineal  during  four  days 
with  20  Cc.  of  alcohol  and  60  Cc.  of  water.     Then  filter.     The  color  of  this 
test  solution  is  turned  violet  by  alkalies,  and  yellowish-red  by  acids. 

(b)  Hematoxylin.     Dissolve  0*2  Gm.  of  hematoxylin  in  100  Cc.  of  alcohol. 
Use  about  5  drops  for  each  titration.     This  indicator  assumes  a  yellow  to 
orange   color   in   acid   solutions,   and    a   violet  to  purple   color   in   alkaline 
solutions.     The    titration   is    complete    when    the   change   in    color  remains 
permanent  upon  the  addition  of  one  drop  of  the  volumetric  solution  after 
stirring  the  liquid. 

(c)  lodeosin.     Dissolve  OT    Gm.   of  iodeosin,   C2oH8l4O5,   in    100    Cc.  of 
alcohol.     This  indicator  becomes  colorless  in  acid  solutions,  changing  to  pink 
in  alkaline  solutions.     For  assaying  alkaloidal  residues  dissolve  the  latter  in  a 
measured  excess  of  volumetric  acid  solution,  and  transfer  the  acid  solution  to 
a  200  Cc.  flask,  washing  the  container  well  with  water  until  the  contents  of 
the  flask  measure  about  100  Cc.     Add  20  Cc.  of  ether  and  5  drops  of  the 
iodeosin  solution,  cork,  and  shake  well.      Then  add  the  volumetric  alkali 
solution    gradually,    shaking    well    after    each    addition.      The    titration    is 
complete  when  the  lower  aqueous  solution  retains  a  faint  pink  color  after 
shaking  thoroughly. 


I98  ANALYSIS   OF  DRUGS,   ETC. 

chloroformic  layer,  rejecting  the  same,  and  then  run  the  acid  aqueous  layer 
into  the  beaker.  Pass  the  combined  acid  aqueous  solutions  through  a  pledget 
of  purified  cotton  into  the  first  separator,  after  cleaning  it  thoroughly,  rinsing 
the  second  separator,  the  beaker,  and  the  funnel  with  about  TO  Cc.  of  distilled 
water.  To  the  first  separator,  add  15  Cc.  of  chloroform,  a  small  piece  of  red 
litmus  paper,  and  enough  ammonia  water  to  produce  a  distinctly  alkaline 
reaction.  Shake  the  separator  for  half  a  minute,  and  when  the  liquids  have 
separated  draw  off  the  chloroformic  layer  into  a  beaker.  Repeat  this  process 
with  two  portions  of  10  Cc.  each  of  chloroform,  and  evaporate  thj  combined 
chloroformic  liquids  in  the  beaker  to  dryness  on  a  water-bath  containing  warm 
water  ;  dissolve  the  residue  in  3  Cc.  of  ether,  and  allow  the  latter  to  evaporate 
completely.  To  the  alkaloidal  residue  add  5  Cc.  of  T^  H2SO4  and  5  drops 
of  hematoxylin  (or  iodeosin),  then  titrate  the  excess  of  acid  with  ~  KHO. 
Divide  the  number  of  cubic  centimeters  of  -£$  KHO  used,  by  5,  subtract  the 
quotient  from  5  (the  5  Cc.  ofy^HjSO*  taken),  and  multiply  the  remainder 
by  0-0287,  and  this  product  by  20,  to  obtain  the  percentage  of  mydriatic 
alkaloids  contained  in  the  extract  of  belladonna  leaves.  The  figure  0^0287 
represents  the  weight  in  Cms.  of  mydriatic  alkaloids  (mainly  atropine) 
required  to  neutralize  i  Cc.  of  -f^  H,2SO4- 

(/)  Assay  of  fluidextract  of  belladonna  root.  Transfer  10  Cc.  of  fluid- 
extract  of  belladonna  root  by  means  of  a  graduated  pipette  to  a  separator,  add 
10  Cc.  of  distilled  water,  20  Cc.  of  chloroform,  and  2  Cc.  of  ammonia  water. 
Shake  the  separator  well  for  one  minute,  and  draw  off  the  lower  chloroformic 
layer  into  a  second  separator.  Repeat  the  extraction  with  two  portions  of 
10  Cc.  each  of  chloroform,  and  draw  the  chloroformic  solution  into  the  second 
separator.  To  the  latter  add  8  Cc.  of  N.  H2SO4  and  20  Cc.  of  distilled  water, 
shaking  well  for  one  minute.  When  perfectly  separated  draw  off  and  reject 
the  lower  chloroformic  layer,  and  filter  the  acid  aqueous  layer  into  a  clean 
separator.  Wash  the  separator  and  filter  with  10  Cc.  of  distilled  water,  adding 
this  to  the  clean  separator.  To  the  latter  add  20  Cc.  of  chloroform  and  4  Cc. 
of  ammonia  water,  and  shake  well  for  several  minutes.  Draw  off  the  lower 
chloroformic  layer  into  a  beaker,  and  repeat  the  extraction  with  two  portions 
of  10  Cc.  each  of  chloroform,  adding  the  chloroformic  solution  to  the  beaker. 
Allow  the  chloroform  in  the  beaker  to  evaporate  on  a  water-bath,  containing 
warm  water,  until  the  residue  is  perfectly  dry.  To  the  alkaloidal  residue  add 
5  Cc.  of  -£$  H2SO4,  and  when  the  residual  alkaloids  have  all  dissolved,  titrate 
the  solution  with  -^  KHO,  using  5  drops  of  hematoxylin  or  iodeosin  as  an 
indicator.  Divide  the  number  of  cubic  centimeters  of  -^  KHO  used,  by  5, 
subtract  the  quotient  from  5  (the  5  Cc.  of  y^  H2SO4),  and  multiply  the 
remainder  by  o'o287,  and  this  product  by  10,  to  obtain  the  weight  in  Cms. 
of  mydriatic  alkaloids  contained  in  one  hundred  cubic  centimeters  of  the  fluid- 
extract  of  belladonna  root. 

(g)  Assay  of  fluidextract  of  hyoscyamus.  Use  50  Cc.  of  the  fluidextract 
and  proceed  as  above  shown  for  fluidextract  of  belladonna  root,  but  finally 
multiplying  the  product  by  2  instead  of  10. 

(h)  Assay  of  fluidextract  of  stramonium.  The  method  to  be  employed  is 
identical  with  that  above  given  for  fluidextract  of  belladonna  root,  using  ten 
cubic  centimeters  of  fluidextract  of  stramonium. 

(/)  Assay  of  tincture  of  belladonna  leaves.  Transfer  100  Cc.  of  tincture  of 
belladonna  leaves  to  an  evaporating  dish  and  evaporate  it  on  a  water-bath 
until  it  measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dis- 
solve any  separated  substance,  and  then  assay  the  resulting  liquid  by  the 
method  above  given  for  fluidextract  of  belladonna  root,  using  the  same  details 
as  there  directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the 
exception  that  the  multiplication  of  the  product  by  10  be  omitted  ;  the  result 


U.S.P.   ASSAYS  OF  DRUGS.  199 

will   represent   the   weight  in  Gms.  of  alkaloids  contained   in    one   hundred 
cubic  centimeters  of  tincture  of  belladonna  leaves. 

(k)  Assay  of  tincture  of  hyoscyamus.  Transfer  100  Cc.  of  tincture  of 
hyoscyamus  to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  it 
measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dissolve  any 
separated  substance,  and  then  assay  the  resulting  liquid  by  the  method  above 
given  for  fluidextract  of  belladonna  root,  using  the  same  details  as  there 
directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the  exception  that 
the  multiplication  by  10  be  omitted ;  the  result  will  represent  the  weight  in 
Gms.  of  alkaloids  contained  in  one  hundred  cubic  centimeters  of  tincture 
of  hyoscyamus. 

(/)  Assay  of  tincture  of  stramonium.  Transfer  100  Cc.  of  tincture  of 
stramonium  to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  it 
measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dissolve  any 
separated  substance,  and  then  assay  the  resulting  liquid  by  the  method  above 
given  for  fluidextract  of  belladonna  root,  using  the  same  details  as  there 
directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the  exception  that 
the  multiplication  by  10,  as  there  directed,  be  omitted ;  the  result  will 
represent  the  weight  in  Gms.  of  alkaloids  contained  in  one  hundred  cubic 
centimeters  of  tincture  of  stramonium. 

(m)  Assay   of  belladonna  plaster  (rubber  base}.     Into   a   suitable    beaker 
containing  50  Cc.  of  chloroform   and   3   Cc.   of  ammonia  water,   introduce 
10  Gm.  of  belladonna  plaster  cut  into  strips.     Stir  until  the  plaster  is  entirely 
removed  from  the  cloth ;  then  pour  off  the  chloroform  into  another  beakerr.. 
wash  the  cloth  with   25    Cc.    of  chloroform  and   i    Cc.    of  ammonia  water 
carefully,  and  add  the  washings  to  the  chloroformic  solution  first  obtained. 
If  necessary,  repeat  the  washing  with  25  Cc.  of  chloroform,  and  add  this  also 
to  the  chloroformic  solution.     Then  dry  the  cloth  at  a  low  temperature ;  cooB 
and  weigh  it,  and  subtract  its  weight  from  the  original  weight  of  the  plaster. 
To  the  chloroformic  solution,   add  four-fifths  of  its  volume   of  alcohol,   stir 
gently,  and  allow  the  liquid  to  stand  until  all  of  the  rubber  has  separated  in  a 
compact  mass.     Then  pour  off  the   supernatant  liquid  into  a  separator  of 
250  Cc.  capacity,  and,  having  prepared  a  solution  of  sulphuric  acid  by  diluting, 
40  Cc.  of  N.  H2SO4  with  60  Cc.  of  distilled  water,  add  20  Cc.  of  the  soluiior^ 
to  the  separator,  and  agitate  for  two  minutes,  rotating  gently.     Draw  off  the 
chloroformic  solution  into  another  separator,  shake  this  with  10  Cc.  of  the 
sulphuric  acid  solution,  and  add  the  acid  solution  to  that  in  the  first  separator.. 
Repeat  until  the  acid  washings  cease  to  give  a  reaction  with  mercuric  potassium* 
iodide  T.S. ;  combine  the  acid  liquids,   and,   having  rendered  this  solution, 
alkaline  with  ammonia  water,  shake  out  the  alkaloids  with  three  successive- 
portions  of  25,  15,  and  10  Cc.  of  chloroform.     Collect  these  in  a  flask,  distill 
off  all   of  the  chloroform  with  the  aid  of  a  water-bath.     To  the  alkaloidal/ 
residue  add  a  slight  excess  of  —j  H2SO4,  noting  the  quantity  used,  and  then, 
add  10  drops  of  chloroform  and,  after  rotating,  evaporate  the  latter  by  means 
of  a  water-bath,     Then  add  5  drops  of  hematoxylin,  and,  rotating,  titrate  the 
excess  of  acid  with  ~~  KHO.     Divide  the  number  of  cubic  centimeters  of 
-^  KHO  used,  by  5,  subtract  the  quotient  from  the  number  of  cubic  centi- 
meters of  ^  H2SO4  first  added,  and  divide  the  difference  by  the  number  of 
Gms.  of  belladonna  plaster  separated  from  the  cloth  ;  multiply  the  quotient 
by  0*0287,  and    this   product    by    100,    which  will   give   the    percentage  of 
mydriatic  alkaloids  in  the  belladonna  plaster. 

(3)  Coca  and  its  Preparations. 

(a)  Assay  of  coca.     Place   10   Gm.  of  coca  in  an   Erlenmeyer  flask,   add 
50  Cc.  of  a  mixture  of  chloroform  i  volume  and  ether  4  volumes,  and  insert 


196  ANALYSIS   OF  DRUGS,   ETC. 

V.  TT.S.P.  ASSAYS  OF  DRUGS  WHERE  THE  RESIDUE  IS  TITRATED. 

(1)  Aconite  and  its  Preparations. 

(a)  Assay  of  aconite.     Introduce   10  Gm.  of  aconite  (in  No.   40   powder) 
into  a  200  Cc.  Erlenmeyer  flask,  add  75  Cc.  of  a  mixture  of  alcohol  7  parts, 
and  distilled  water  3  parts  (by  volume),  stopper  the  flask  securely,  and  agitate 
it  at  intervals  during  four  hours.     After  placing  a  pledget  of  cotton  in  the 
bottom  of  a  small  cylindrical  glass  percolator  (25  Mm.  in  diameter),  carefully 
transfer  the  contents  of  the  flask  to  the  percolator.     When  the  liquid  has  all 
passed  through,  continue  the  percolation  with  more  of  the  same  mixture  until 
150  Cc.  of  percolate  have  been  obtained.     Pour  the  percolate  into  a  shallow 
porcelain  evaporating  dish,  and  evaporate  it  to  dryness  at  a  temperature  not 
exceeding  60°  C.  (140°  F.).     Add  5  Cc.  of  ^  H2SO4  and  10  Cc.  of  distilled 
water.     When  the  extract  is  dissolved,  filter  the  liquid  into  a  separator,  washing 
the  dish  and  filter  with  about  40  Cc.  of  distilled  water,  and  add  the  washings 
to  the  separator.     Add  25  Cc.  of  ether  and  2  Cc.  of  ammonia  water  to  the 
separator,  and  agitate  it  for  one  minute.     Draw  off  the  lower  layer  into  a 
flask,  and  filter  the  ether-solution  into  a  beaker.     Return  the   contents  of 
the  flask  to  the  separator,  add  15  Cc.  of  ether,  and  again  agitate  it  for  one 
minute.     Draw  off  the  lower  layer  into  the  flask,  and  filter  the  ether-solution 
into  the  beaker.     Repeat  the  shaking  out  with  two  other  portions  of  10  Cc. 
each  of  ether.      Evaporate   the   combined   ether-solutions  to  dryness,  and 
dissolve  the  residue  in  3  Cc.  of  —^  H2SO4,  diluted  with  20  Cc.  of  distilled 
water.     Add  to  the  solution   5  drops    of  hematoxylin    indicator,   and   then 
carefully  run  in  -~$  KHO  until  a  violet  color  is  produced,  the  transition  stages 
being  as  follows  :  first  yellow,  then  green,  finally  passing  into  violet.     Divide 
the  number  of  Cc.  of  -£$  KHO  used,  by  5,  subtract  this  number  from  3  (the 
3  Cc.  of  j^  H2SO4  taken),  multiply  the  remainder  by  0*064,  and  this  product 
by  10,  which  will  give  the  percentage  of  aconitine  in  the  aconite. 

(b)  Assay  of  fluidextract  of  aconite.      Transfer  TO  Cc.  of  fluidextract  of 
aconite  by  means  of  a  graduated  pipette  to  a  porcelain  dish,  and  evaporate 
it  carefully  to  dryness  on  a  water-bath  at  a  temperature  not  exceeding  60°  C. 
(140°  F.).     Add  5  Cc.  of  £>  H2SO4  and  10  Cc.  of  distilled  water.     When  the 
extract  is  dissolved,  filter  the  liquid  into  a  separator,   washing  the  dish  and 
filter  with  about  40  Cc.  of  distilled  water  and  adding  the  washings  to  the 
separator.     From   this  point  proceed  as  instructed  for  the  assay  of  aconite 
until  the  titration  is  complete.     Finally  divide  the  number  of  Cc.  of  ^  KHO 
used,   by   5,   subtract  this  number  from  3  (the  3  Cc.  of  TN^  H2SO4  taken), 
multiply  the  remainder  by  0-064,  and  this  product  by  10,  which  will  give  the 
weight   in   Gms.  of  aconitine  contained  in  one  hundred  cubic  centimeters  of 
the  fluidextract  of  aconite. 

(c)  Assay  of  tincture  of  aconite.     Transfer  100  Cc.  of  tincture  of  aconite  to 
an  evaporating  dish  and  evaporate  it  carefully  to  dryness  at  a  temperature  not 
exceeding  60°  C.  (140°  F.),  and  assay  the  resulting  extract  by  the  method 
above  given  for  the  fluidextract,  using  the  same  details  as  there  directed  for 
10  Cc.  of  fluidextract  of  aconite,  with  the  exception  that  the  multiplication  of 
the    product   by  10  must  be  omitted;   the  result  will  represent  the  weight 
in  Gms.  of  aconitine  contained  in  one  hundred,  cubic  centimeters  of  tincture  of 
aconite. 

(2)  Assays  of  Drugs  containing  Mydriatic  Alkaloids. 

(a)  Assay  of  belladonna  leaves.  Place  10  Gm.  of  belladonna  leaves  (in 
No.  60  powder)  in  an  Erlenmeyer  flask,  and  add  50  Cc.  of  a  mixture  of 
chloroform  i  part  and  ether  4  parts  (both  by  volume).  After  inserting  the 


U.S.P.    ASSAYS  OF  DRUGS.  iq; 

stopper  securely,  allow  the  flask  to  stand  ten  minutes,  then  add  2  Cc.  of 
ammonia  water  mixed  with  3  Cc.  of  distilled  water,  and  shake  the  flask  well 
at  frequent  intervals  during  one  hour.  Then  transfer  as  much  as  possible  of 
the  contents  of  the  flask  to  a  small  percolator  which  has  been  provided  with 
a  pledget  of  cotton  packed  firmly  in  the  neck  and  inserted  in  a  separator 
containing  6  Cc.  of  N.  H,SO4  diluted: with  20  Cc.  of  distilled  water.  When 
the  liquid  has  passed  through  the  cotton,  pack  the  belladonna  leaves  firmly  in 
the  percolator  with  the  aid  of  a  glass  rod,  and  having  rinsed  the  flask  with 
10  Cc.  of  the  chloroform-ether  mixture,  transfer  the  remaining  contents  of 
the  flask  to  the  percolator,  by  the  aid  of  several  small  portions  (5  Cc.)  of  the 
chloroform-ether  mixture,  and  continue  the  percolation  with  successive  small 
portions  of  the  same  liquid  (using  in  all  50  Cc.).  Next,  shake  the  separator 
well  for  one  minute,  after  securely  inserting  the  stopper,  and  when  the  liquids 
have  completely  separated,  draw  off  the  acid  solution  into  another  separator. 
Add  to  the  chloroform-ether  mixture  10  Cc.  of  sulphuric  acid  mixture  of  the 
same  strength  as  that  previously  used,  agitate  well,  and  again  draw  off  the  acid 
solution  into  the  second  separator ;  repeat  this  operation  once  more,  drawing 
off  the  acid  solution  as  before ;  introduce  into  the  acid  solutions  contained  in 
the  second  separator  a  small  piece  of  red  litmus  paper,  then  add  ammonia 
water  until  the  liquid  is  distinctly  alkaline,  and  shake  out  with  three  successive 
portions  of  chloroform  15,  15,  and  5  Cc.;  collect  the  chloroform  solutions  in  a 
beaker,  place  it  on  a  water-bath  containing  warm  water,  and  allow  the  chloroform 
to  entirely  evaporate.  Dissolve  the  residue  in  3  Cc.  of  ether,  and  let  this  also 
evaporate  completely.  To  the  alkaloidal  residue  add  3  Cc.  of  TNF  H2SO4  and 
5  drops  of  hematoxylin  (or  iodeosin),  then  titrate  the  excess  of  acid  with 
-/u  KHO  potassium  hydroxide.  Divide  the  number  of  cubic  centimeters 
of  TNg-  KHO  used,  by  5,  subtract  the  quotient  from  3  (the  3  Cc..  of  y^  H2SO4 
taken),  and  multiply  the  remainder  by  0*0287  and  this  product  by  10;  the 
result  will  be  the  percentage  of  total  mydriatic  alkaloids  contained  in  the 
belladonna  leaves. 

(b)  Assay  ofscopola.  The  method  to  be  employed  is  identical  with  that  given 
above  for  belladonna  leaves,  using  ten  Gins,  of  scopola,  in  No.  60  powder. 

(f)  Assay  of  hyoscyamus.  The  method  to  be  employed  is  identical  with 
that  given  above  for  belladonna  leaves,  with  the  exception  that  tiventy-five 
Gms.  of  hyoscyamus,  in  No.  60  powder,  are  to  be  used,  the  quantity  of 
chloroform-ether  mixture  which  is  added  at  first  increased  from  50  Cc.  to 
TOO  Cc.,  and  the  product  at  the  end  of  the  assay  multiplied  by  4  instead  of  TO. 

(d)  Assay  of  stramonium.     The  method  to  be  employed  is  identical  with 
that  given  above  for  belladonna  leaves,  using  ten  Gms.  of  stramonium,  in 
No.  60  powder. 

(e)  Assay  of  extract  of  belladonna   leaves.     Introduce   5    Gm.   extract  of 
belladonna  leaves  into  a  small  beaker  and  dissolve  it  in  a  mixture  consisting 
of  alcohol  5  Cc.,  distilled  water  10  Cc.,  ammonia  water  2  Cc.,  and  chloroform 
20  Cc.     When  dissolved,  transfer  it  to  a  separator,  rinsing  the  beaker  with  a 
little  alcohol  and  adding  the  rinsings  to  the  separator.     Insert  the  stopper 
securely,  and  shake  the  separator  for  half  a  minute.     Draw  off  the  chloroformic 
layer  into  a  second  separator,  and  add  to  the  first  separator  ro  Cc.  more  of 
chloroform.     Shake  it  for  half  a  minute,  allow  to  separate,  and  again  draw 
off  the  chloroformic  layer  into  the  second  separator.     Repeat  this  with  10  Cc. 
more   of  chloroform.     To    the    united    chloroformic    liquids    in   the   second 
separator,  add  5   Cc.  of  N.  H2SO4  and   10  Cc.  of  distilled  water,  and  shake 
it  for  half  a  minute.     Draw  off  the  chloroformic  layer,  after  the  liquids  have 
separated,   into    the    first    separator,    after   cleaning   it    thoroughly,   and   the 
aqueous  layer  into  a  beaker,  and  repeat  the  process  by  adding  to  the  first 
separator   10  Cc.  of  distilled  water  and   i   Cc.  of  N.  H2SO4.     Draw  off  the 


I98  ANALYSIS   OF  DRUGS,   ETC. 

chloroformic  layer,  rejecting  the  same,  and  then  run  the  acid  aqueous  layer 
into  the  beaker.  Pass  the  combined  acid  aqueous  solutions  through  a  pledget 
of  purified  cotton  into  the  first  separator,  after  cleaning  it  thoroughly,  rinsing 
the  second  separator,  the  beaker,  and  the  funnel  with  about  TO  Cc.  of  distilled 
water.  To  the  first  separator,  add  15  Cc.  of  chloroform,  a  small  piece  of  red 
litmus  paper,  and  enough  ammonia  water  to  produce  a  distinctly  alkaline 
reaction.  Shake  the  separator  for  half  a  minute,  and  when  the  liquids  have 
separated  draw  off  the  chloroformic  layer  into  a  beaker.  Repeat  this  process 
with  two  portions  of  10  Cc.  each  of  chloroform,  and  evaporate  the  combined 
chloroformic  liquids  in  the  beaker  to  dry  ness  on  a  water-bath  containing  warm 
water  ;  dissolve  the  residue  in  3  Cc.  of  ether,  and  allow  the  latter  to  evaporate 
completely.  To  the  alkaloidal  residue  add  5  Cc.  of  •£$  H2SO4  and  5  drops 
of  hematoxylin  (or  iodeosin),  then  titrate  the  excess  of  acid  with  -^  KHO. 
Divide  the  number  of  cubic  centimeters  of  ^j  KHO  used,  by  5,  subtract  the 
quotient  from  5  (the  5  Cc.  of  ^  H2SO4  taken),  and  multiply  the  remainder 
by  0-0287,  and  this  product  by  20,  to  obtain  the  percentage  of  mydriatic 
alkaloids  contained  in  the  extract  of  belladonna  leaves.  The  figure  0-0287 
represents  the  weight  in  Cms.  of  mydriatic  alkaloids  (mainly  atropine) 
required  to  neutralize  i  Cc.  of  T^  H,,SO4. 

(f)  Assay  of  fluidextract  of  belladonna    roof.     Transfer    10  Cc.    of  fluid- 
extract  of  belladonna  root  by  means  of  a  graduated  pipette  to  a  separator,  add 
10  Cc.  of  distilled  water,  20  Cc.  of  chloroform,  and  2  Cc.  of  ammonia  water. 
Shake  the  separator  well  for  one  minute,  and  draw  off  the  lower  chloroformic 
layer  into  a  second  separator.     Repeat  the  extraction  with  two  portions  of 
10  Cc.  each  of  chloroform,  and  draw  the  chloroformic  solution  into  the  second 
separator.     To  the  latter  add  8  Cc.  of  N.  H2SO4  and  20  Cc.  of  distilled  water, 
shaking  well  for  one  minute.     When  perfectly  separated  draw  off  and  reject 
the  lower  chloroformic  layer,  and  filter  the  acid  aqueous  layer  into  a  clean 
separator.     Wash  the  separator  and  filter  with  10  Cc.  of  distilled  water,  adding 
this  to  the  clean  separator.     To  the  latter  add  20  Cc.  of  chloroform  and  4  Cc. 
of  ammonia  water,  and  shake  well  for  several  minutes.     Draw  off  the  lower 
chloroformic  layer  into  a  beaker,  and  repeat  the  extraction  with  two  portions 
of  10  Cc.  each  of  chloroform,  adding  the  chloroformic  solution  to  the  beaker. 
Allow  the  chloroform  in  the  beaker  to  evaporate  on  a  water-bath,  containing 
warm  water,  until  the  residue  is  perfectly  dry.     To  the  alkaloidal  residue  add 
5  Cc.  of  ~Q  H2SO4,  and  when  the  residual  alkaloids  have  all  dissolved,  titrate 
the  solution  with  -£•$  KHO,  using  5  drops  of  hematoxylin  or  iodeosin  as  an 
indicator.     Divide  the  number  of  cubic  centimeters  of  -£$  KHO  used,  by  5, 
subtract  the  quotient  from  5    (the   5    Cc.   of  ~$  H2SO4),   and  multiply  the 
remainder  by  0*0287,  and  this  product  by  10,  to  obtain  the  weight  in  Cms. 
of  mydriatic  alkaloids  contained  in  one  hundred  cubic  centimeters  of  the  fluid- 
extract  of  belladonna  root. 

(g)  Assay  of  fluidextract  of  hyoscyamus.     Use  50   Cc.   of  the  fluidextract 
and  proceed  as  above  shown  for  fluidextract  of  belladonna  root,  but  finally 
multiplying  the  product  by  2  instead  of  10. 

(h)  Assay  of  fluidextract  of  stramonium.  The  method  to  be  employed  is 
identical  with  that  above  given  for  fluidextract  of  belladonna  root,  using  ten 
cubic  centimeters  of  fluidextract  of  stramonium. 

(j)  Assay  of  tincture  of  belladonna  leaves.  Transfer  100  Cc.  of  tincture  of 
belladonna  leaves  to  an  evaporating  dish  and  evaporate  it  on  a  water-bath 
until  it  measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dis- 
solve any  separated  substance,  and  then  assay  the  resulting  liquid  by  the 
method  above  given  for  fluidextract  of  belladonna  root,  using  the  same  details 
as  there  directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the 
exception  that  the  multiplication  of  the  product  by  10  be  omitted  ;  the  result 


U.S.P.   ASSAYS  OF  DRUGS.  199 

will   represent   the   weight  in  Gms.  of  alkaloids  contained   in    one   hundred 
cubic  centimeters  of  tincture  of  belladonna  leaves. 

(k)  Assay  of  tincture  of  hyoscyamus.  Transfer  100  Cc.  of  tincture  of 
hyoscyamus  to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  it 
measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dissolve  any 
separated  substance,  and  then  assay  the  resulting  liquid  by  the  method  above: 
given  for  fluidextract  of  belladonna  root,  using  the  same  details  as  there 
directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the  exception  that 
the  multiplication  by  10  be  omitted ;  the  result  will  represent  the  weight  ira 
Gms.  of  alkaloids  contained  in  one  hundred  cubic  centimeters  of  tincture 
of  hyoscyamus. 

(/)  Assay  of  tincture  of  stramonium.  Transfer  100  Cc.  of  tincture  of 
stramonium  to  an  evaporating  dish,  and  evaporate  it  on  a  water-bath  until  it 
measures  about  10  Cc.  Add,  if  necessary,  sufficient  alcohol  to  dissolve  any 
separated  substance,  and  then  assay  the  resulting  liquid  by  the  method  above 
given  for  fluidextract  of  belladonna  root,  using  the  same  details  as  there 
directed  for  10  Cc.  of  fluidextract  of  belladonna  root,  with  the  exception  that 
the  multiplication  by  10,  as  there  directed,  be  omitted ;  the  result  will 
represent  the  weight  in  Gms.  of  alkaloids  contained  in  one  hundred  cubic 
centimeters  of  tincture  of  stramonium. 

(m)  Assay   of  belladonna  plaster  (rubber  base).     Into   a   suitable   beaker 
containing  50  Cc.  of  chloroform    and   3   Cc.   of  ammonia  water,   introduce 
10  Gm.  of  belladonna  plaster  cut  into  strips.     Stir  until  the  plaster  is  entirely" 
removed  from  the  cloth ;  then  pour  off  the  chloroform  into  another  beakery. 
wash  the  cloth  with   25    Cc.    of  chloroform  and   i    Cc.    of  ammonia  water 
carefully,  and  add  the  washings  to  the  chloroformic  solution  first  obtained.. 
If  necessary,  repeat  the  washing  with  25  Cc.  of  chloroform,  and  add  this  also 
to  the  chloroformic  solution.     Then  dry  the  cloth  at  a  low  temperature;  cooli 
and  weigh  it,  and  subtract  its  weight  from  the  original  weight  of  the  plaster. 
To  the  chloroformic  solution,   add  four-fifths  of  its  volume   of  alcohol,   stir 
gently,  and  allow  the  liquid  to  stand  until  all  of  the  rubber  has  separated  in  a 
compact  mass.     Then  pour  off  the   supernatant  liquid  into  a  separator  of 
250  Cc.  capacity,  and,  having  prepared  a  solution  of  sulphuric  acid  by  diluting; 
40  Cc.  of  N.  H2SO4  with  60  Cc.  of  distilled  water,  add  20  Cc.  of  the  solution* 
to  the  separator,  and  agitate  for  two  minutes,  rotating  gently.     Draw  off  the 
chloroformic  solution  into  another  separator,  shake  this  with  10  Cc.  of  the 
sulphuric  acid  solution,  and  add  the  acid  solution  to  that  in  the  first  separator.. 
Repeat  until  the  acid  washings  cease  to  give  a  reaction  with  mercuric  potassium  - 
iodide  T.S. ;  combine  the  acid  liquids,   and,   having  rendered  this  solution, 
alkaline  with  ammonia  water,  shake  out  the  alkaloids  with  three  successive- 
portions  of  25,  15,  and  10  Cc.  of  chloroform.     Collect  these  in  a  flask,  distil 
off  all  of  the  chloroform  with  the  aid  of  a  water-bath.     To  the  alkaloida^ 
residue  add  a  slight  excess  of  ~  H2SO4,  noting  the  quantity  used,  and  then, 
add  10  drops  of  chloroform  and,  after  rotating,  evaporate  the  latter  by  means 
of  a  water-bath.     Then  add  5  drops  of  hematoxylin,  and,  rotating,  titrate  the 
excess  of  acid  with  -^  KHO.     Divide  the  number  of  cubic  centimeters  of 
-J-Q  KHO  used,  by  5,  subtract  the  quotient  from  the  number  of  cubic  centi- 
meters of  £j  H2SO4  first  added,  and  divide  the  difference  by  the  number  of 
Gms.  of  belladonna  plaster  separated  from  the  cloth  ;  multiply  the  quotient 
by  o'028y,   and   this   product    by    100,    which  will    give   the    percentage   of 
mydriatic  alkaloids  in  the  belladonna  plaster. 

(3)  Coca  and  its  Preparations. 

(a)  Assay  of  coca.     Place   10   Gm.  of  coca  in  an   Erlenmeyer  flask,   ado! 
50  Cc.  of  a  mixture  of  chloroform  i  volume  and  ether  4  volumes,  and  insert 


200  ANALYSIS   OF  DRUGS,   ETC. 

the  stopper  securely.  Allow  the  flask  to  stand  ten  minutes,  then  add  2  Cc. 
of  ammonia  water  mixed  with  3  Cc.  of  distilled  water,  and  shake  the  flask 
well,  at  frequent  intervals,  during  one  hour.  Then  transfer  as  much  as  possible 
of  the  contents  of  the  flask  to  a  small  percolator  which  has  been  provided 
with  a  pledget  of  cotton  packed  firmly  in  the  neck,  and  inserted  in  a  separator 
containing  6  Cc.  of  N.  H2SO4  diluted  with  20  Cc.  of  distilled  water.  When 
the  liquid  has  passed  through  the  cotton,  pack  the  coca  firmly  in  the  perco- 
lator with  the  aid  of  a  glass  rod,  and,  having  rinsed  the  flask  with  10  Cc.  of 
chloroform-ether  mixture,  transfer  the  remaining  contents  of  the  flask  to  the 
percolator  by  the  aid  of  several  small  portions  (5  Cc.)  of  a  chloroform-ether 
mixture,  using  the  same  proportions  as  before,  and  continue  the  percolation 
with  successive  small  portions  of  the  same  liquid  (in  all  50  Cc).  Next,  shake 
the  separator  well  for  one  minute,  after  securely  inserting  the  stopper,  and 
when  the  liquids  have  completely  separated,  draw  off  the  acid  liquid  into 
another  separator.  Add  to  the  chloroform-ether  mixture  10  Cc.  of  a  sulphuric 
acid  mixture,  using  the  same  proportions  as  before,  agitate  well  and  again 
draw  off  the  acid  liquid.  Repeat  this  operation  once  more,  drawing  off  the 
acid  solution  as  before  into  the  second  separator,  introduce  a  small  piece  of 
red  litmus  paper,  add  ammonia  water  until  the  liquid  is  distinctly  alkaline, 
and  shake  out  with  3  successive  portions  of  ether  (25,  20,  and  15  Cc.). 
Collect  the  ether-solutions  in  a  beaker,  place  it  on  a  water-bath  filled  with 
warm  water,  and  allow  the  ether  to  evaporate  entirely.  Dissolve  the  residue 
in  3  Cc.  of  ether,  and  let  this  also  evaporate.  To  the  alkaloidal  residue  add 

4  Cc.   of  YQ-   H2SO4  and  5  drops  of  hematoxylin  or  iodeosin,   then  titrate 
the    excess   of  acid    with  -^j-  KHO.     Divide  the   number   of  cubic  centi- 
meters of  -2$   KHO   used,    by   5,  subtract   this  number  from  4  (the  4  Cc. 
of  Y0-  H2SO4  taken),  and  multiply  the  remainder  by  0*03  and  this  product 
by    10,    to  obtain   the   percentage   of  ether-soluble    alkaloids   contained   in 
the  coca. 

(b)  Assay  of  fluidextract  of  coca.  Transfer  10  Cc.  of  fluidextract  of  coca 
foy  means  of  a  graduated  pipette  to  a  separator,  add  25  Cc.  of  ether,  and  then 
2  Cc.  of  ammonia  water,  shaking  together  for  one  minute.  When  the  liquids 
have  completely  separated,  draw  off  the  lower  aqueous  layer  into  a  second 
separator,  and  to  this  add  20  Cc.  more  of  ether,  and  repeat  the  shaking  for 
one  minute.  Draw  off  and  reject  the  lower  aqueous  layer  from  the  second 
separator,  and  add  the  ether-layer  to  the  first  separator.  To  this  separator 
now  add  5  Cc.  of  N.  H2SO4  and  5  Cc.  of  distilled  water,  and  shake  it  well  for 
one  or  two  minutes.  After  the  liquids  have  separated,  draw  off  the  lower 
aqueous  layer  into  the  other  separator,  and  repeat  the  extraction  in  the  first 
separator  with  9  Cc.  of  distilled  water  and  i  Cc.  of  N.  H2SO4,  shaking  the 
liquids  for  one  minute,  and  separating  as  before.  Add  the  aqueous  solution 
to  the  other  separator,  and  reject  the  ether.  Now  add  to  the  combined  acid 
liquids  20  Cc.  of  ether,  a  small  piece  of  red  litmus  paper,  and  sufficient 
ammonia  water  to  render  the  mixture  distinctly  alkaline,  and  shake  the  liquids 
for  one  or  two  minutes.  Draw  off  the  separated  aqueous  layer  into  the  other 
separator  and  the  ether-layer  into  a  beaker.  Repeat  the  extraction  of  the 
aqueous  layer  in  the  other  separator  with  two  portions  (15  Cc.  each)  of  ether, 
and  add  the  resulting  ether-solutions  to  the  beaker.  Now  evaporate  the  ether 
from  the  beaker,  and,  when  dry,  add  to  it  5  Cc.  of  ~$  H2SO4,  and  stir  until 
the  alkaloidal  residue  is  dissolved.  Then  add  5  drops  of  hematoxylin  or 
iodeosin,  and  titrate  the  excess  of  acid  with  ^  KHO.  Divide  the  number  of 
cubic  centimeters  of  ~$  KHO  used,  by  5,  subtract  this  number  from  5  (the 

5  Cc.  of  Yff   H2SO4  taken),  and  multiply  the  remainder  by  0^03,  and  this 
product  by  10,  to  obtain  the  weight  in  Gins,  of  ether-soluble  alkaloids  contained 
in  one  hundred  cubic  centimeters  of  the  fluidextract  of  coca. 


U.S. P.   ASSAYS   OF  DRUGS.  201 

(4)  Ipecac  and  its  Preparations. 

(a)  Assay  of  ipecac.     Introduce  15  Gm.  of  ipecac  (in  No.  80  powder)  into 
an  Erlenmeyer  flask  of  250  Cc.  capacity,  add   115  Cc.  of  ether  and  35  Cc. 
of  chloroform,  shake  the  flask  during  five  minutes,  and  then  add  3  Cc.  of 
ammonia  water  and  again  shake  the  flask  at  intervals  during  half  an  hour. 
Now  add  10  Cc.  of  distilled  water,  shake  the  liquid  until  the  powder  collects 
in  masses,  and  pour  off  100  Cc.  of  the  clear  ethereal  solution  into  a  measuring 
cylinder.      Transfer   the    latter   to   a   separator,    add    10  Cc.   of   N.  H2SO4 
and   10    Cc.    of  distilled   water.       Shake    the   separator   moderately   during 
two  minutes,  and  when  the  liquids  have  separated,  draw  off  the  lower  acid 
solution   into  a  second  separator.     Repeat   the  shaking   out    of  the  ether- 
solution  with  3  Cc.  of  N.  H2SO4  and  5  Cc.  of  distilled  water,  drawing  the 
acid  solution  into  the  second  separator.     Repeat  the  shaking  out  again,  using 
10  Cc.  of  distilled  water,  and  add  the  aqueous  solution  to  the  second  separator. 
Reject  the  ether  in  the  first  separator,  introduce  a  small  piece  of  red  litmus 
paper    into    the    second  separator,    add    enough   ammonia   water  to  render 
the    liquid   alkaline,    and    25    Cc.   of  ether,   and    then   shake   the  separator 
vigorously   during  one  minute ;  draw    off  the  alkaline  aqueous   liquid  into 
another  separator,  and  transfer  the  ether-solution  to  a  flask.     Add  20  Cc.  of 
ether  to  the  alkaline  liquid  in  the  separator,  shake  it  for  one  minute,  and, 
having  allowed  the  liquids  to  separate,  draw  off  the  alkaline  liquid  into  the 
other  separator,  and  transfer  the  ether-solution  to  the  flask.     Again  shake  out 
the  alkaline  liquid  with  10  Cc.  of  ether,  and,  when  the  fluids  have  separated, 
reject  the  alkaline  liquid  and  add  the  ether-solution  to  the  liquid  in  the  flask. 
Distil  the   ether  from  the  flask  with  the  aid  of  a  water- bath,  and  dissolve 
the  alkaloidal  residue  in  12  Cc.  of  ^y  H2SO4,  warming  it  gently  on  a  water- 
bath  if  necessary.     Then  add   five  drops    of  hematoxylin   and  titrate  with 
TTQ  KHO.     Divide  the  number  of  cubic  centimeters  of  TN^KHO  used,  by  5, 
subtract  the  quotient  from   12  (the   12  Cc.  of  ^5- H2SO4  taken),  and  multiply 
the  remainder  by  0*0238,  and  this  product  by  10,  which  will  give  the  per- 
centage of  alkaloids  in  the  ipecac. 

(b)  Assay  of  fluidextract  of  ipecac.     Transfer  10  Cc.  of  fluidextract  of  ipecac 
by  means  of  a  graduated  pipette  to  a  porcelain  evaporating  dish.     Evaporate 
off  the  alcohol  with  the  aid  of  a  water-bath,  and,  when  almost  cool,  add  5  Cc. 
N.  H2SO4,  and  stir  the  liquid  at  intervals  for  three  minutes.     Filter  the  liquid 
into  a  separator,  rinse  the  dish,  and  wash  the  filter  successively  with  10  Cc. 
and  5  Cc.  of  distilled  water,  and  add  these  liquids  to  the  separator.     To  the 
separator  add  20  Cc.  of  ether  and  a  small  piece  of  red  litmus  paper ;  render 
the  liquid  alkaline  with  ammonia  water   and  shake  the   separator  for   one 
minute.     Draw  off  the  aqueous  layer  into  a  beaker,  and  the  ether-layer  into 
another  beaker.     Return  the  aqueous  solution  to  the  separator,  add  10  Cc. 
more  of  ether,  and  shake  the  liquid,  adding  the  ether-solution  to  that  already 
in  the  beaker,  and  returning  the  aqueous  solution  to  the  separator ;  repeat 
the  extraction  with  10  Cc.  more  of  ether,  and  then  add  the  ether-layer  to  that 
already  in  the   beaker.     Allow  the  combined   ether-solutions   to  evaporate, 
either  spontaneously  or  with  the  aid  of  a  water-bath  containing  warm  water, 
and  then  add  10  Cc.  of—  H2SO4.     Stir  the  liquid  carefully  with  a  glass  rod 
to  facilitate  the  solution  of  the  alkaloids,  and  when  these  have  all  dissolved, 
add    5    drops   of   hematoxylin.     From    a   graduated    burette,    add   sufficient 
^  KHO  to  just  cause  the  yellow  color  of  the  solution  to  turn  purple.     Divide 
the  number  of  cubic  centimeters  of  -j^  KHO  used,  by  5,  subtract  the  quotient 
from  10  (the  10  Cc.  of  yjy  H^SO4  taken),  and  multiply  the  remainder  by  o'o238, 
and  this  product  by    TO,  which   will  give   the  weight   in  Gms.   of  alkaloids 
contained  in  each  one  hundred  cubic  centimeters  of  fluidextract  of  ipecac. 


202  ANALYSIS   OF  DRUGS,   ETC. 

(5)  Nux  Vomica  and  its  Preparations. 

(a)  Assay  of  nnx  vomica.     Introduce  20  Gm.  of  nux  vomica  (in  No.  60 
powder)  into  a  250  Cc.  Erlenmeyer  flask  and  add  to  it  200  Cc.  of  a  mixture  of 
137-5  Cc.  of  ether,  44  Cc.  of  chloroform,  i3'5  Cc.  of  alcohol,  and  5  Cc.  of 
ammonia  water ;    insert  the   stopper   securely   and    macerate  with    frequent 
shaking  during  one  hour  and  allow  it  to  stand  in  a  cool  place  for  twelve 
hours.     Decant  into  a  measuring  cylinder  100  Cc.  of  the  liquid  (representing 
10  Gm.  of  nux  vomica),  and  pour  this  into  a  separator,  preferably  of  a  globular 
shape.     Rinse  the  cylinder  with  a  little  chloroform,  add  this  to  the  separator, 
and  then  add  15  Cc.  of  N.  H2SO4 ;  shake  the  mixture  moderately  during  one 
minute,  being  careful  to  avoid  emulsification  ;  when  the  liquids  have  separated 
completely,  draw  off  the  acid  liquid  into  a  beaker.     Repeat  the  shaking  out 
with  successive  portions  of  5  and  3  Cc.  of  N.  H2SO4 ;  collect  the  acid  solu- 
tions and  pour  them  into  a  separator.     If  a  drop  of  the  last  acid  solution 
yields  a  precipitate  with  mercuric  potassium  iodide,  repeat  the  shaking  out 
of  the  ether  solution  with  5  Cc.  of  N.  H2SO4.     To  the  combined  acid  solu- 
tions  in  the   separator  add  a  small  piece   of  red  litmus   paper,   25  Cc.  of 
chloroform,  and  then  sufficient  ammonia  water  to  render  the  liquid  alkaline, 
and  shake  the  separator  thoroughly.     When  the  liquids  have  separated  draw 
off  the  chloroform  into  a  flask  of  100  Cc.  capacity,  and  repeat  the  shaking  out 
of  the  alkaline  liquid  with  two  successive  portions  of  15  Cc.  each  of  chloro- 
form, adding  the  latter  to  that  already  in  the  flask.     Evaporate  the  combined 
chloroformic    solutions    in    the    flask   until   the    alkaloidal    residue    is    dry, 
then    dissolve   in    it   15    Cc.    of   sulphuric   acid    (3    per   cent.),   warming   it 
on  a  water-bath.     When  the   solution  has  cooled,  add  3  Cc.   of  a  cooled 
mixture  of  equal  volumes  of  nitric  acid  (specific  gravity  1*40)  and  distilled 
water,  and  after  rotating  the  liquid  a  few  times,  set  it  aside  for  exactly  ten 
minutes,  shaking  it  gently   three  times   during  this  interval.     Transfer  the 
resulting  red  liquid  to  a  separator  containing  25  Cc.  of  an  aqueous  solution  of 
sodium  hydroxide  (i  in   10)  and  wash  the  flask  three  times  with  very  small 
amounts  of  distilled  water,  and  add  the  washings  to  the  separator.     If  the 
liquid  is  not  turbid  add  2  Cc.  more  of  the  solution  of  sodium  hydroxide. 
Now  add   20   Cc.   of  chloroform   to  the  separator,  and  shake   it  well  by  a 
rotating  motion  for  a  few  minutes,  allow  the  liquids  to  separate,  and  draw 
off  the  chloroform,  through  a  small  filter  wetted  with  chloroform,  into  a  flask. 
Repeat  this  twice,  using  10  Cc.  of  chloroform  each  time,  and  draw  off  both 
portions  into  the  flask,  using  the  same  filter.    Finally,  wash  the  filter  and  funnel 
with  5  Cc.  of  chloroform,  and  then  evaporate  all  the  chloroform  by  means  of 
a  water-bath  very  carefully,  to  avoid  decrepitation.     To  the  alkaloidal  residue 
add  6  Cc.  of  -£$  H2SO4,  5  drops  of  iodeosin,  about  80  Cc.  of  distilled  water, 
and  20  Cc.  of  ether.     When  all  the  alkaloid  is  dissolved,  titrate  the  excess  of 
acid  with  -^j  KHO  until  the  aqueous  liquid  just  turns  pink.    Divide  the  number 
of  cubic  centimeters  of  J^  KHO  used,  by  5,  subtract  this  number  from  6  (the 
6  Cc.  of  T^H2SO4  taken),  multiply  the  remainder  by  0*0332,  and  this  product 
by  TO,  which  will  give  the  percentage  of  strychnine  in  the  nux  vomica. 

(b)  Assay  of  extract  of  ?iux  vomica.  Introduce  2  Gm.  of  extract  of  nux 
vomica  into  a  beaker,  and  dissolve  it  in  25  Cc.  of  a  mixture  of  16  Cc.  of 
ether,  5  Cc.  of  chloroform,  and  4  Cc.  of  ammonia  water.  When  dissolved, 
transfer  it  to  a  separator,  rinsing  the  beaker  with  a  little  chloroform,  and 
adding  the  rinsings  to  the  separator.  Insert  the  stopper  securely  and  shake 
the  separator  carefully  for  a  few  minutes.  Draw  off  the  aqueous  layer  into 
another  separator,  washing  the  ether-solution  and  separator  with  a  little  water, 
and  adding  this  to  the  second  separator.  Then  shake  out  the  aqueous  liquid 
with  two  portions  of  15  and  10  Cc.,  respectively,  of  chloroform,  and  add  these 
to  the  first  separator.  If  a  few  drops  of  the  liquid  left  in  the  second  separator 


U.S. P.   ASSAYS  OF  DRUGS.  203 

still  give  a  reaction  with  mercuric  potassium  iodide  after  acidulating,  repeat 
the  shaking  out  with  10  Cc.  more  of  chloroform.  Now  shake  out  the  chloro- 
formic  solution  in  the  first  separator  with  three  portions  of  15,  10,  and  10  Cc. 
of  sulphuric  acid  solution  (3  per  cent.),  and  collect  the  combined  acid  solu- 
tions in  another  separator.  Introduce  a  small  piece  of  red  litmus  paper,  add 
enough  ammonia  water  to  render  the  liquid  alkaline,  and  extract  the  mixture 
with  three  portions,  respectively,  of  15,  10,  and  10  Cc.  of  chloroform.  Draw 
off  the  chloroformic  solutions  into  a  beaker,  and  evaporate  the  chloroform 
with  the  aid  of  a  water-bath.  Dissolve  the  alkaloidal  residue  in  the  beaker  in 
15  Cc.  of  3  per  cent,  sulphuric  acid  solution  by  the  aid  of  a  water-bath.  From 
this  point  proceed  by  adding  HNO3  and  extracting  the  alkaloid  by  CHCla  in 
the  presence  of  NaHO,  as  directed  above  in  the  assay  of  nux  vomica,  until 
the  alkaloidal  residue  is  obtained.  To  the  alkaloidal  residue  add  10  Cc.  of 
iNJy  H.;SO4,  5  drops  of  iodeosin,  about  90  Cc.  of  distilled  water,  and  20  Cc.  of 
ether.  When  all  the  alkaloid  is  dissolved,  titrate  the  excess  of  acid  with  ^  KHO 
until  the  aqueous  liquid  just  turns  pink.  Divide  the  number  of  cubic  centimeters 
of  yjj-  KHO  used,  by  5,  subtract  this  number  from  10  (the  10  Cc.  of  TNff  H2SO4 
taken),  multiply  the  remainder  by  0*0332,  and  this  product  by  50,  which  will 
give  the  percentage  of  strychnine  contained  in  the  extract  of  nux  vomica. 

(c]  Assay  of  fluidextract  of  nux  vomica.     Transfer  10  Cc.  of  fluidextract  of 
nux  vomica  by  means  of  a  graduated  pipette  to  a  porcelain  dish,  evaporate 
it  to  dryness  with  the  aid  of  a  water-bath,  and  dissolve  the  residue,  while 
warm,  in  a  mixture  of  16  Cc.  of  ether,  5  Cc.  of  chloroform,  and  4  Cc.  of 
ammonia  water,  and  transfer  the  solution  to  a  separator,  rinsing  the  dish  with 
a  little  chloroform,  which  is  to  be  added  to  the  separator,  and  shake  the 
separator  carefully  for  a  few  minutes.     When  the  fluids  have  separated,  draw 
off  the  aqueous  layer  into  another  separator,  wash  the  chloroform-ether  liquid 
and  separator  with  a  little  water,  and  add  this  to  the  second  separator.     Then 
shake  the  aqueous  liquid  with  two  successive  portions  of  15  and  10  Cc.  respec- 
tively of  chloroform,  and  add  these  to  the  first  separator.     If  a  small  portion 
of  the  liquid  left  in  the  second  separator  still  shows,  after  acidifying,  a  reaction 
with  mercuric  potassium  iodide,  repeat  the  shaking  out  with  10  Cc.  more  of 
chloroform.     Now  shake   the   combined   liquids   in   the   first  separator  with 
three  successive  portions,  respectively,  of  15,    10,  and  10  Cc.  ol  N.  H2SO4, 
and  collect  the  combined  acid  solutions  in  another  separator.     To  this  acid 
solution  add   a   small   piece    of  red  litmus  paper,    and    sufficient   ammonia 
water  to  render  it  alkaline,  then  shake  out  successively  with  three  portions, 
respectively,  of  25,  10,  and  10  Cc.  of  chloroform,  and  collect  the  chloroform- 
solutions  in  a  beaker.     Evaporate  the  chloroform  with  the  aid  of  a  water- 
bath,  dissolve  the  alkaloidal  residue  in  15  Cc.  of  3  per  cent,  sulphuric  acid 
solution,  by  the  aid  of  a  water-bath,  and  allow  the  liquid  to  cool.     From  this 
point  proceed  by  adding  HNOs  and  extracting  the  alkaloid  by  CHC13  in  the 
presence  of  NaHO,  as  directed  above  in  the  assay  of  nux  vomica,  until  the  alka- 
loidal residue  is  obtained.    To  the  alkaloidal  residue  add  loCc.  of  ^  H2SO4, 
5  drops  of  iodeosin,  about  80  Cc.  of  distilled  water,  and  20  Cc.  of  ether. 
When  all  the  alkaloid  is  dissolved,  titrate  the  excess  of  acid  with  -^  KHO, 
until  the  aqueous  liquid  just  turns  pink.     Divide  the  number  of  cubic  centi- 
meters of  ^  KHO  taken,  by  5,  subtract  this  number  from  10  (the   10  Cc.  of 
j^  H2SO4  taken),  multiply  the  remainder  by  0^0332,  and  this  product  by  10, 
which  will  give  the  weight  in  Cms.  of  strychnine  in  100  Cc.  of  the  fluidextract. 

(d)  Assay  of  tincture  of  nux  vomica.     Transfer  100  Cc.  of  tincture  of  nux 
vomica  to  a  porcelain  dish,  evaporate  it  to  dryness  on  a  water-bath,  and  assay 
the  resulting  extract  by  the  method  above  given  for  extract  of  nux  vomica, 
using  the  same  details  as  there  directed  for  2  Gm.  of  extract  of  nux  vomica, 
with  the  exception  that  the  multiplication  by  50  be  omitted  ;  the  result  will 


204  ANALYSIS   OF  DRUGS,   ETC. 

represent  the  weight  in  Cms.  of  strychnine  contained  in  one  hundred  cubic 
centimeters  of  tincture  of  nux  vomica. 

(6)  Pilocarpus  and  its  Preparations. 

(a)  Assay  of  pilocarpus.    Moisten  10  Gin.  of  pilocarpus  with  2  Cc.  of  ammonia 
water  and  3  Cc.  of  chloroform,  and  at  once  pack  it  firmly  in  a  small  cylindrical 
percolator,  which  has  been  provided  with  a  pledget  of  cotton  packed  firmly  in 
the  neck.    Percolate  the  powder  slowly  with  chloroform  containing  about  2  per 
cent,  of  ammonia  water,  until  it  is  exhausted,  about   TOO  Cc.  of  menstruum 
usually  being  sufficient.     Pour  into  a  separator  the  percolate,  and  shake  it 
out  with  15  Cc.  of  N.  H2SO4,  transferring  the  acid  aqueous  layer  to  another 
separator,  and  repeating  the  shaking  out  of  the  chloroform-solution  with  2  Cc. 
of  N.  H2SO4,  mixed  with  8  Cc.  of  distilled  water.     Add  the  acid  layer  to  the 
second  separator,  and  again  repeat  the  shaking  out  with   10  Cc.  of  distilled 
water,  and  add  the  aqueous  liquid  to  the  second  separator.     Introduce  into 
the  second  separator  a  small  piece  of  red  litmus  paper,  add  enough  ammonia 
water  to  render  the  liquid  alkaline,  and  shake  out  the  liquid  with  20  Cc.  of 
chloroform,  drawing  off  the  chloroformic  solution  into  a  beaker.     Repeat  the 
shaking  out  with  two  portions  of  15  and  10  Cc.  each  of  chloroform,  and  add 
the  chloroformic  solutions  to  the  beaker.    Evaporate  the  chloroform  by  means 
of  a  water-bath,  and  dissolve  the  alkaloidal  residue  in  7  Cc.  of  y^  H2SO4.    Add 
5  drops  of  cochineal  or  iodeosin,  and  titrate  the  excess  of  acid  with  ~  KHO. 
Divide  the  number  of  cubic  centimeters  of  ^  KHO  used,  by  5,  subtract  the 
quotient  from  7  (the  7  Cc.  of  ^  H9SO4  taken),  and  multiply  the  remainder  by 
o'02,  and  this  product  by  10;  the  result  will  be  the  percentage  of  alkaloids 
contained  in  the  pilocarpus.    The  figure  0*02  represents  the  weight   in  Gms. 
of  alkaloids  (mainly  pilocarpine)  required  to  neutralize  i  Cc.  of  —$  H2SO4. 

(b)  Assay  of  fluidextract  of  pilocarpus.     Transfer  TO  Cc.  of  fluidextract  of 
pilocarpus  by  means  of  a  graduated  pipette  to  a  porcelain  dish  containing  a 
little  clean  sand,  and  evaporate  it  to  dryness  with  the  aid  of  a  water-bath. 
Mix    the   sand   uniformly  with  the  extract  and  transfer  the   mixture  to  an 
Erlenmeyer  flask  of  about  100  Cc.  capacity,  rinsing  the  dish  with  a  mixture 
of  25  Cc.  of  chloroform  and  2-5  Cc.  of  ammonia  water.     Transfer  the  rinsings 
to  the  flask,  cork  it  securely,  and  shake  it  well  at  intervals  during  one  hour. 
Decant  the  liquid,  transfer  to  a  separator,  wash  the  sand  with  several  portions 
of  chloroform,  draw  off  and  filter  the  chloroformic  liquid  into  another  separ- 
ator.     Then   shake    out  the  chloroform-solution  with    15  Cc.  of  N.  H2SO4, 
transferring   the   acid   aqueous    solution    to  another  separator.      Repeat    the 
shaking  out  with  a  mixture  of  5  Cc.  of  N.  H2SO4  and  5  Cc.  of  distilled  water, 
collecting  the  acid    solutions    in    the    second    separator.     Again    repeat    the 
shaking  out  with  10  Cc.  of  distilled  water,  and  add  the  aqueous  liquid  to  the 
second  separator.     Introduce  into  the  second  separator  a  piece  of  red  litmus 
paper,  and  proceed  to  shake  out  with  ammonia  water  and  CHCls,  all  as  above 
directed  to  obtain  the  alkaloidal  residue.     Dissolve  the  alkaloidal  residue  in 
8  Cc.  of  f\  H2SO4.     Add  5  drops  of  cochineal  or  iodeosin,  and  titrate  the 
excess  of  acid  with  -^  KHO.     Divide  the  number  of  cubic  centimeters  of 
/F  KHO  used,  by  5,' subtract  the  quotient  from  8  (the  8  Cc.   of  -^  H,SO4 
taken),  and  multiply  the  remainder  by  0*02,  and  this  product  by  10,  to  obtain 
the  weight  in  Gms.  of  alkaloids  contained  in  one  hundred  cubic  centimeters  of 
the  fluidextract  of  pilocarpus. 

(7)  Physostigma  and  its  Preparations. 

(a)  Assay  of  physostigma.  Introduce  20  Gm.  of  physostigma  into  an 
Erlenmeyer  flask  of  about  250  Cc.  capacity,  add  200  Cc.  of  ether,  and  shake 
the  flask  well  during  ten  minutes.  Then  add  10  Cc.  of  an  aqueous  solution 
of  sodium  bicarbonate  (i  in  20),  and  shake  the  mixture  vigorously  at  intervals 


U.S.P.    ASSAYS   OF  DRUGS  205 

during  four  hours.  Allow  the  powder  to  settle,  and  decant  100  Cc.  of  the 
ether-solution  (representing  10  Gm.  of  physostigma)  into  a  measuring  cylinder  ; 
then  transfer  it  to  a  separator,  introduce  a  small  piece  of  blue  litmus  paper, 
and  add  sufficient  N.  H2SO4  to  render  the  liquid  acid,  and  then  10  Cc.  of 
distilled  water.  Shake  the  liquid  well  for  several  minutes,  and  draw  off  the 
aqueous  layer  into  another  separator.  Repeat  the  extraction,  using  2  Cc.  of 
N.  H2SO4  and  8  Cc.  of  distilled  water,  add  the  acid  aqueous  layer  to  the 
second  separator,  and  finally  again  shake  out  the  ether-solution,  using  i  Cc. 
of  N.  H2SO4  and  9  Cc.  of  distilled  water,  adding  this  also  to  the  second 
separator.  To  the  combined  acid  liquids  in  the  second  separator,  add  25  Cc. 
of  ether,  a  small  piece  of  red  litmus  paper,  and  sufficient  sodium  bicarbonate 
solution  (i  in  20)  to  render  it  alkaline.  Shake  the  separator  for  one  minute, 
allow  the  liquids  to  separate,  and  draw  off  the  ether  into  a  beaker.  Repeat 
the  shaking  out  process  with  20  Cc.  and  again  with  15  Cc.  of  ether  added  to 
the  separator,  shake  each  time  for  one  minute,  allow  the  liquids  to  separate, 
and  draw  off  the  ether  into  the  beaker.  Carefully  evaporate  the  ether  from 
the  combined  solutions  by  means  of  a  water-bath,  and  when  dry,  dissolve  the 
residue  in  5  Cc.  of  ~  H2SO4  and  20  Cc.  of  ether,  which  must  be  strictly 
neutral,  and  transfer  this  solution  to  a  bottle,  rinsing  with  80  Cc.  of  water;  add 
5  drops  of  iodeosin,  and  titrate  the  excess  of  acid  with  ~  KHO,  until,  after 
shaking,  the  aqueous  liquid  just  acquires  a  pink  color.  Divide  the  number  of 
cubic  centimeters  of  -£$  KHO  used,  by  5,  subtract  the  quotient  from  5  (the 
5  Cc.  of  j^j  H2SO4  taken),  and  multiply  the  remainder  by  0*0273,  and  this- 
product  by  10;  the  result  will  be  the  percentage  of  alkaloids  soluble  in  ether 
contained  in  the  physostigma.  The  figure  0*0273  represents  the  weight  in  Gins, 
of  alkaloids  (mainly  physostigmine)  required  to  neutralize  i  Cc.  of  ^  H2SO4. 

(b)  Assay  of  extract  of  physostigma.     Transfer  i  Gm.  of  extract  of  physos- 
tigma to  a  small  porcelain  dish,  add  5  Cc.  of  diluted  alcohol,  and  digest  for 
five  minutes  in  a  water-bath  below  boiling  temperature  ;  then  add  about  5  Gm. 
of  very  clean,  fine  quartz  sand,  and  evaporate  to  dryness  on  a  water-bath,, 
triturating  thoroughly  with  a  pestle  to  secure  uniform  admixture.     When  dry, 
carefully  transfer  the  contents  of  the  dish  to  an  Erlenmeyer  flask,  add  100  Cc. 
of  ether,  and  shake  the  flask.     Then  add   10  Cc.  of  an  aqueous  solution  of 
sodium  bicarbonate  (i  in  20),  and  shake  the  contents  vigorously  at  intervals 
for  one  hour.     Allow  the  mixture  to  stand,  and,  when  settled,  decant  50  Cc. 
of  the  ether-solution  into  a  separator,  to  which  add  a  small  piece  of  blue 
litmus  paper,  sufficient  N.  H2SO4  to  render  the  liquid  acid,  and  10  Cc.  of 
distilled  water.     From  this  point  proceed  as  for  physostigma  (commencing 
from  "  shake  the  liquid  well ")  until  the  alkaloidal  residue  is  obtained.    Dissolve 
this  residue  in  2  Cc.  of  y^  H2SO4 ;  rinse  the  solution  carefully  into  a  200  Cc. 
flask  with  distilled  water,  add  enough  distilled  water  to  bring  the  volume  to 
about  90  Cc.,  add  25  Cc.  of  ether,  and,  having  shaken  the  flask,  add  5  drops- 
of  iodeosin,  then  titrate  the  excess  of  acid  with  -£$  KHO,  until,  after  shaking,, 
the  aqueous  liquid  just  acquires  a  pink  color.     Divide  the  number  of  cubic 
centimeters  of  -^  KHO  used,  by  5,  subtract  the  quotient  from  2  (the  2  Cc. 
of  yjj-  H2SO4  taken),  and  multiply  the  remainder  by  0*0273,  an(^  tms  product 
by  200 ;  the  result  will  be  the  percentage  of  ether-soluble  alkaloids  contained 
in  the  extract  of  physostigma. 

(c)  Assay   of  tincture  of  physostigma.      Transfer    100    Cc.  of  tincture  of 
physostigma  to  a  porcelain  dish,  evaporate  it  to  dryness  on  a  water-bath,  and 
assay  the  resulting  extract  by  the  method  given  above,  using  the  same  details 
as  there  directed  for  i  Gm.  of  extract  of  physostigma,  with  the  exception  that 
the  product  must  be  multiplied  by  2  instead  of  200  ;  the  result  will  represent 
the  weight  in  Gms.  of  ether-soluble  alkaloids  from  physostigma  contained  in 
one  hundred  cubic  centimeters  of  tincture  of  physostigma. 


208 


ANALYSIS   OF  DRUGS,   ETC. 


distilled  water  added  to  make  the  liquid  measure  10  Cc.  If  the  alcohol  be  already  diluted,  a 
correspondingly  larger  volume  of  it  should  be  taken  and  diluted  to  10  Cc.,  so  that  the  pro- 
portion of  alcohol  in  the  liquid  shall  not  be  more  than  about  10  per  cent.,  by  volume.  A 
copper  wire  spiral  (made  by  winding  I  meter  of  No.  18  clean  copper  wire  closely  around  a 
glass  rod  7  millimeters  thick,  making  a  coil  about  3  centimeters  long,  the  end  of  the  wire 
being  formed  into  a  handle)  should  be  heated  to  redness  in  a  flame  free  from  soot,  and 
plunged  steadily  quite  to  the  bottom  of  the  liquid  in  the  test-tube  and  held  there  for  a  second 
or  two,  then  withdrawn  and  dipped  into  water  to  cool.  This  treatment  with  red-hot  copper 
should  be  repeated  five  or  six  times,  immersing  the  test-tube  in  cold  water  to  keep  down  the 
temperature  of  the  liquid.  The  contents  of  the  test-tube  should  now  be  filtered  into  a  wide 
test-tube  and  boiled  very  gently.  If  the  odor  of  acetaldehyde  be  perceptible,  the  boiling  is 
to  be  continued  until  the  odor  ceases  to  be  distinguished  clearly.  The  liquid  is  now  cooled, 
and  to  it  should  be  added  I  drop  of  a  solution  containing  I  part  of  resorcinol  in  200  parts  of 
water.  A  portion  of  this  liquid  is  then  poured  cautiously  into  a  second  tube  containing  pure 
sulphuric  acid,  in  such  a  way  that  the  two  liquids  shall  not  mix,  the  tube  being  held  in  an 
inclined  position  ;  this  tube  is  allowed  to  stand  for  three  minutes,  and  then  slowly  rotated. 
No  rose-red  ring  should  show  at  the  line  of  contact  of  the  two  layers  (absence  of  more  than 
2  per  cent,  of  methyl  alcohoi). 


X.  ANALYSIS  OF  FIXED  OILS  AND  FATS. 

This  is  a  matter  requiring  the  greatest  practice  and  experience,  and, 
unfortunately,  it  is  still  possible  so  to  sophisticate  dearer  with  cheaper  oils  as 
to  practically  defy  definite  analysis.  If,  however,  we  confine  our  attention  to 
the  ordinary  fixed  oils  of  the  U.S. P.,  we  can  get  a  very  fair  idea  of  their  purity, 
or  otherwise,  by  applying  the  following  methods  : — 


(i)  Specific  Gravity,     (a)  In  the  case  of  oils,  this  is  taken  at  25°  C. 
gravities  of  the  U.S. P.  oils  are — 


The 


Almond 
Castor  . 
Cod  liver 
Cotton  seed 
Croton 
Lard  oil 
Linseed 
Olive    . 


•90510-915 

'945       '905 
•918 

•915 
'935 
'90S 
•925 
•910 


•922 
•921 
•950 
•915 
'935 
•915 


(b)  In  the  case  of  solid  fats  we  melt  them,  and  take  their  gravity  either  at 
40°  C.  or  at  the  boiling  point  of  water.  The  U.S. P.  uses  the  former  standard, 
but  for  a  person  not  continually  operating  with  oils,  the  latter  is  more  likely  to 
give  good  results,  and  may  be  worked  in  the  following  manner  :— 

Take  an  ordinary  specific-gravity  bottle  with  a  well-fitting  perforated  stopper, 
and  also  a  deep  basin  capable  of  holding  a  good  deal  more  water  than  will 
quite  cover  the  bottle.  Charge  the  basin  with  distilled  water,  and  put  it  over 
a  good  gas  flame,  so  that  it  is  rapidly  heated  to  boiling  point. 

Melt  the  fat,  and  charge  the  specific-gravity  bottle  with  it  in  the  usual  way, 
and  then,  holding  it  with  a  pair  of  wooden  tongs,  plunge  it  into  the  water  so 
that  it  lies  on  its  side,  entirely  immersed,  with  its  neck  pointing  downwards. 
The  melted  fat  expands,  and,  passing  through  the  hole  in  the  stopper, 
absolutely  prevents  the  entrance  of  any  of  the  water,  which  must  be  kept 
briskly  boiling  for  twenty  minutes.  The  bottle  is  then  fished  out,  rapidly 
wij,ed  dry,  cooled,  and  weighed.  The  weight  of  the  empty  bottle  having 
been  deducted,  the  balance  gives  the  weight  of  fat  it  holds  at  the  temperature 
of  boiling  water,  which,  divided  by  the  weight  of  water  that  the  bottle  holds 
under  the  same  conditions,  gives  a  sufficiently  accurate  gravity  for  all  ordinary 
purposes.  Thus  treated  the  following  solid  fats  give — 


ANALYSIS  OF  FIXED   OILS  AND  FATS.  209 

Butter -867  to  '870 

Lard -860  ,,  -861 

Cacao  butter '857  ,,  '858 

Beef  fat -857  ,,  '859 

(2)  Hubl's  Method  of  Iodine  Absorption.     The  iodine  value  or  number  of 
a  fat  or  an  oil  is  a  figure  which  indicates  the  percentage  of  iodine  absorbed 
under  certain   conditions.     It  is  determined  as  follows : — To  a  solution  of 
0*3  Gm.  of  oil  in  10  Cc.  of  chloroform  contained  in  a  glass-stoppered  bottle 
of  250  Cc.  capacity,  add  25  Cc.  of  a  mixture  of  equal  volumes  of  alcoholic 
iodine  (25  Gm.  I  in  500  Cc.  alcohol),  and  alcoholic  mercuric  chloride  (30  Gm. 
HgCl2  in  500  Cc.  alcohol),  both  of  which  have  been  measured  from  a  burette. 
After  having  been  securely  stoppered,  the  bottle  is  set  aside  in  a  cool  place, 
protected  from  the  light,  for  a  period  of  four  hours.     After  this  time,  the 
mixture  must  still  possess  a  brown  color;  if  it  does  not,  a  further  measured 
portion  of  the  mixture  of  the  two  reagents  should  be  added,  and  the  mixture 
be  again  set  aside.     Finally,  20  Cc.  of  a  20  per  cent,  solution  of  potassium 
iodide  are  added,  followed  by  50  Cc.  of  water,  and  -^  Na2S2O3  is  then  added 
in  small  successive  portions,  shaking  thoroughly  after  each  addition  until  the 
color  of  the  mixture  is  discharged.     The  number  of  Cc.  of  -^  Na2S2Os  con- 
sumed is  noted.     At  the  same   time  that  this  test  is  carried  out,  a  blank 
experiment   is   made  in  which  exactly  the   same   quantities  of  chloroform, 
iodine,  and  mercuric  chloride  are  mixed,  and,  after  standing  for  four  or  more 
hours,   the   free  iodine  is    estimated  by  titration  as  directed  above.      The 
number  of  Cc.  of  ^  Na2S2O3  consumed  is  noted,  and  from  this  is  deducted 
the  number  of  Cc.  which  was  consumed  in  the  test;  the  difference  multiplied 
by  1 2  -5 9,  and  this  product  divided  by  3,  gives  the  iodine  value  of  the  fat  or 
oil.     In  dealing  with  linseed  oil  only  '15  Gm.  should  be  taken,  the  bottle 
should  be  allowed  to  stand  for  sixteen  hours,  and  the  product  divided  by  1-5 
instead  of  by  3.     With  solid  fats,  such  as   Ol.  Theobroma,  *8  Gm.  is  to  be 
taken  and  the  product  divided  by  8.     Thus  treated,  the  following  oils  and 
fats  show : — 

Per  cent,  of  iodine  absorbed. 

Almond 95  to  100 

Castor 86         89 

Cod  liver 140 

Cotton       ......  102 

Croton       ....'..  100 

Lard  oil     .         .          .         .         .  56 

Linseed 170 

Olive 80 

Cacao  butter       .         .         .  33 

(3)  Saponification  Equivalent.     The  determination  of  the  saponification 
value  is  conducted  as  follows  : — Weigh  out  accurately,  in  a  flask  holding  150 
to  200  Cc.,  1-5  to  2  Gm.  of  the  purified  and  filtered  fat.     Next  run  into  the 
flask,  with  a  burette,  25  Cc.  of  alcoholic  potassium  hydroxide  (28  Gm.  KHO 
in    1000  Cc.  alcohol).     While  exactly  25  Cc.  is  not  indispensable,  in  com- 
parative tests  precisely  the  same  amount  must  be  used,  allowing  the  burette 
to  drain  in  exactly  the  same  way  in  each  test.     Then  place  a  small  funnel  in 
the  flask  and  heat  it  on  a  water-bath  containing  boiling  water,  for  half  an 
hour,  so  that  the  alcohol  is  simmering,  frequently  imparting  a  rotatory  motion 
to  the  contents  of  the  flask.     Then  add  i  Cc.  of  phenol-phthalein,  and  titrate 
back  the  excess  of  KHO  with  §  HC1.     A  blank  test  is  made  at  the  -same 
time,  using  the  25  Cc.  of  alcoholic  KHO  alone;  the  difference  in  the  number 
of  Cc.  of  J  HC1  c'onsumed  by  the  blank  test  and  the  real  test,  multiplied  by 
27-87,  and  divided  by  the  weight  in  grammes  of  the  fat  or  oil  taken,  will  give 
the  saponification  equivalent  of  the  sample  tested. 


150 
1 08 

105 

74 

187 

88 

38 


210  ANALYSIS   OF  DRUGS,   ETC, 

The  following  are  the  saponification  equivalents  of  the  oils  referred  to : — 

Per  cent,  of  KHO  neutralized. 
Almond     .          .         .         .          .  191  to  200 

Castor        ......      179  ,,  180 

Cod  liver 175    ,  18' 


Cotton       ......  191 

Croton       ......  212 

Linseed 187 

Olive          ......  191 

Lard  oil     ......  195 

Cacao  butter  188 


190 
218 
195 
195 
197 

195 


(4)  Specific  Heating  Power.  The  process  consists  in  placing  50  Gm.  of 
the  oil  or  melted  fat  in  a  glass  cylinder,  immersing  a  thermometer,  noting 
the  temperature,  and  then  causing  10  Cc.  of  strong  sulphuric  acid,  brought 
to  exactly  the  same  temperature  as  that  of  the  oil,  to  flow  slowly  in  from  a 
stoppered  burette,  stirring  with  the  thermometer  all  the  time,  and  noting  the 
extreme  point  to  which  the  mercury  rises.  The  experiment  is  then  repeated 
•under  exactly  the  same  conditions,  using  50  Cc.  of  distilled  water  instead  of  oil, 
and  the  rise  is  again  noted.  Lastly,  the  rise  in  temperature  observed  with 
the  oil  is  divided  by  that  shown  with  the  water.  The  stopper  of  the  burette 
should  be  so  set  that  it  takes  exactly  one  minute  to  deliver  10  Cc.  of  acid. 
The  following  are  some  characteristic  results  : — 

Water        .  I  -oo 


Castor 
Cod  liver 
Cotton 
Linseed 
Olive 


0'89  to  0-92 
2-46  „  272 
1-63  ,,  170 
3'2o  „  3-49 
o  89  „  0-94 


The  rise  is  so  great  with  linseed  oil,  that  it  is  best  to  work  upon  it  after 
diluting  it  one  half  with  a  mineral  oil,  previously  found  to  give  only  a  slight 
definite  rise,  and  to  make  a  correction. 

(5)  Qualitative  Tests  for  TT.S.P.  Fixed  Oils  and  Fats. 

(a)  Almond  oil.  (i)  Remains  clear  at — IO°C.,  and  does  not  congeal  until  cooled  to  nearly 
— 20°  C.  (absence  of  olive  oil  or  lard  oil}. 

(2)  2  Cc.  vigorously  shaken  with  i  Cc.  of  fuming  nitric  acid  and  i  Cc.  of  water  forms  a 
whitish  mixture,  which,  after  standing  for  some  hours  at  about  10°  C.  (50°  F.),  separates 
into  a  solid,  white  mass  and  a  slightly  colored  liquid  (distinction  from  oils  of  peach  and  apricot 
kernels •,  which  give  a  red  color,  and  sesame  and  cotton  seed  oils,  which  are  colored  brown). 

(3)  10  Cc.  mixed  with   15  Cc.  of  solution  of  sodium  hydroxide  (i   in  6)  and  10  Cc.  of 
alcohol,  and  the  mixture  allowed  to  stand  at  a  temperature  of  35°  to  40°  C.,  with  occasional 
agitation,   until  it  becomes  clear,  and  then  diluted  with  100  Cc.  of  water,  yields  a  clear 
solution  which,  on  adding  an  excess  of  hydrochloric  acid,  will  throw  up  a  layer  of  oleic  acid. 
This,  when  separated  from  the  aqueous  liquid,  washed  with  warm  water,  and  clarified  by 
heating  on  a  water-bath,  will  remain -liquid  if  cooled  to  15°  C.     This  acid,  when  mixed  with 
an  equal  volume  of  alcohol,  should  yield  a  clear  solution,  which  at  15°  C.  should  not  deposit 
any  fatty  acids,  nor  become  turbid  upon  the  further  addition  of  I  volume  of  alcohol  (dis- 
tinction from  olive,  arachis,  cotton  seed,  sesame,  and  other  fixed  oils}. 

(b}  Castor  oil.  (i)  Soluble  in  all  proportions  in  absolute  alcohol,  and  in  glacial  acetic 
acid,  and  in  3  times  its  volume  of  92*5  per  cent,  alcohol. 

(2)  3  Cc.  shaken  for  a  few  minutes  with  3  Cc.  of  carbon  disulphide  and  I  Cc.  of  sulphuric 
acid,  should  not  acquire  a  blackish-brown  color  (absence  oft.  foreign  oils}. 

(c}  Cod  liver  oil.  (i)  Very  slightly  soluble  in  alcohol,  but  readily  soluble  in  ether, 
chloroform,  or  carbon  disulphide  ;  also  in  2-5  parts  of  acetic  ether. 

(2)  I   drop  of  the  oil  dissolved  in  20  drops  of  chloroform  and  shaken  with  I  drop  of 
sulphuric   acid,    will   give   a   violet-red    tint,    rapidly   changing   to    rose-red    and,    finally, 
brownish-yellow. 

(3)  If  a  glass  rod  moistened  with  sulphuric  acid  be  drawn  through  a  few  drops  of  the  oil, 
on  a  porcelain  plate,  a  violet  color  will  be  produced. 

(4)  If  two  or  3  drops  of  fuming  nitric  acid  be  allowed  to  flow  alongside  of  10  or  15  drops 
of  the  oil,  contained  in  a  watch-glass,  a  red  color  will  be  produced  at  the  point  of  contact. 
On  Stirling  the  mixture  with  a  glass  rod,  this  color  becomes  bright  rose-red,  soon  changing 
to  lemon-yellow  (distinction  from  seal  oil,  which  shows  at  first  no  change  of  color,  and  from 
other  fish  oils,  which  become  at  first  blue  and  afterwards  brown  and  yellow). 


ANALYSIS  OF  FIXED   OILS  AND  FATS.  211 

(d)  Cotton  seed  oil.     (i)  On  cooling  the  oil  to  a  temperature  below  12°  C.,  particles  of 
solid  fat  will  separate.     At  about  o°  to — 5°  C. ,  the  oil  becomes  nearly  or  quite  Solid. 

(2)  6  Cc.  of  the  oil  thoroughly  shaken  for  ten  minutes  with  a  mixture  of  I  '5  Cc.  of  nitric- 
acid  and  o'5  Cc.  of  water,  then  heated  in  a  bath  of  boiling  water  for  not  more  than  fifteen 
minutes,  will  assume  an  orange  or  reddish-brown  color,  and  will  form  a  semi-solid  mass  in 
twelve  hours  at  ordinary  temperature. 

(3)  5  Cc.  thoroughly  shaken  in  a  test-tube  with  5  Cc.  of  an  alcoholic  solution  of  silver 
nitrate  (o-i  Gm.  of  silver  nitrate  in  10  Cc.  of  alcohol  and  2  drops  of  nitric  acid),  and  then 
heated  for  about  five  minutes  on  a  water-bath,  will  assume  a  red  or  reddish-brown  color. 

(4)  If  2  Cc.  be  mixed  in  a  test-tube  with  I  Cc.  each  of  amyl  alcohol  and  carbon  disulphide 
containing  I  per  cent,  of  sulphur  in  solution,  and  the  test-tube  be  immersed  to  one-third  or 
one-half  its  depth  in  boiling  salt  water,  a  red  color  will  develop  in  from  ten  to  fifteen 
minutes. 

(e)  Croton  oil.     (i)  When  gently  heated  with  twice  its  volume  of  absolute  alcohol,  it 
forms  a  clear  solution  from  which  the  croton  oil  should  separate  on  cooling. 

(2)  If  2  Cc.  be  mixed  with  i  Cc.  of  fuming  nitric  acid  and  i  Cc.  of  water  and  then 
vigorously  shaken,  it  should  not  solidify,  even  partially,  after  standing  two  days  (absence  of 
other  non-drying  oils). 

(/)  Lard  oil.  (i)  At  a  temperature  a  little  below  10°  C.  (50°  F.),  it  usually  commences 
to  deposit  a  white,  granular  fat,  and  at  or  near  o°  C.  (32°  F.),  it  forms  a  solid  white  mass. 

(2)  Tested  for  the  presence  of  cotton  seed  oil,  as  above  directed  by  tests  (3)  and  (4),  none 
should  be  found. 

(3)  Should  be  completely  saponifiable  with  alcoholic  potassium  hydroxide  and  the  resulting 
soap  entirely  soluble  in  water,  without  separation  of  an  oily  layer  (absence  of  mineral  oils). 

(g)  Linseed  oil.  (i)  It  does  not  congeal  at  temperatures  above— 20°  C.,  and  is  soluble 
in  about  10  parts  of  absolute  alcohol,  and  in  all  proportions  in  ether,  chloroform,  petroleum 
benzin,  carbon  disulphide,  and  oil  of  turpentine. 

(2)  Should   be   completely   saponifiable   with   alcoholic    potassium   hydroxide,    and   the 
resulting  soap  entirely  soluble  in  water  without  leaving  an  oily  residue  (absence  of  mineral 
oils  and  rosin  oil). 

(3)  If  2  Cc.  of  the  oil  be  warmed  and  shaken  in  a  test-tube  with  an  equal  volume  of  glacial 
acetic  acid,  and  if  to  this  mixture,  after  cooling,  i  drop  of  sulphuric  acid  be  added,  a  greenish 
color  should  be  produced  (a  violet  color  under  these  circumstances  indicates  the  presence 
of  rosin  or  rosin  oils). 

(h)  Olive  oil.  (i)  When  cooled  to  from  8°  to  10°  C.,  the  oil  becomes  somewhat  cloudy 
from  the  separation  of  crystalline  particles,  and  at  o°  C.  it  forms  a  whitish  granular  mass. 

(2)  If  2  Cc.  of  olive  oil  be  shaken  vigorously  with  an  equal  volume  of  nitric  acid  (sp.  gr. 
I'37)>  tne  oil  should  retain  a  light  yellow  color,  not  becoming  orange  or  reddish-brown,  and 
after  standing  for  six  hours  should  change  into  a  yellowish-white  solid  mass  and  an  almost 
colorless  liquid  (absence  of  appreciable  quantities  of  cotton  seed  oil  and  most  other  seed  oils). 

(3)  Tested  for  the  presence  of  cotton  seed  oil  by  the  tests  (3)  and  (4)  above  given,  none 
should  be  found. 

(4)  If  2  Cc.  of  the  oil  be  mixed  with  i  Cc.  of  hydrochloric  acid  (sp.  gr.  ri8)  containing 
I  per  cent,  of  sugar,  and  the  mixture  be  shaken  for  half  a  minute  and  allowed  to  stand  for 
five  minutes,  and  then  3  Cc.  of  water  added  and  the  whole  again  shaken,  the  acid  layer 
shou'd  not  show  a  pink  color  (absence  of  sesame  oil). 

(z)  Cacao  butter  (theobroma).  (i)  Is  brittle  at  temperatures  below  15°  C.,  and  melts  at 
30°  to  35°  C.  It  is  readily  soluble  in  ether,  chloroform,  or  benzene  ;  also  soluble  in  100  parts 
of  cold  absolute  alcohol,  and  in  20  parts  of  boiling  absolute  alcohol ;  the  solutions  should  be 
neutral  to  test  paper. 

(2)  If  i  Gm.  of  oil  of  theobroma  be  dissolved  in  3  Cc.  of  ether  in  a  test-tube  at  a  tem- 
perature of  17°  C.,  and  the  tube  frequently  plunged  into  water  at  o°  C.,  the  liquid  should  not 
become  turbid  nor  deposit  white  flakes  in  less  than  three  minutes  ;  and  if  the  mixture  after 
congealing  be  again  brought  to  15°  C.,  it  should  gradually  form  a  perfectly  clear  liquid 
(absence  of  wax,  stearin,  tallow,  etc.). 

(/6)Q  Lard,  (i)  Specific  gravity  :  about  0*917  at  25°  C.,  and  about  0*904  at  40°  C.,  water 
at  25  C.  taken  as  the  standard.  It  melts  at  38°  to  40°  C.  to  a  perfectly  clear  liquid,  which 
is  colorless  in  thin  layers  and  from  which  an  aqueous  layer  should  not  separate. 

(2)  Tested  for  the  presence  of  cotton  s^ed  oil  as  above  (employing  tests  (3)  and  (4),  and 
applying  them  to  5  Cc.  of  melted  and  filtered  lard  while  still  warm),  none  should  be  found. 

(1)  Wool-fat,     (i)  Melts  at  about  40°  C.,  and  at  a  higher  temperature  vaporizes,   the 
vapor  igniting  and  burning  with  a  luminous,  sooty  flame. 

(2)  The  solution  of  wool-fat  in  chloroform  (i  in  50),  when  poured  upon  the  surface  of 
concentrated   sulphuric  acid,  gradually  develops  a  deep  brownish-red  color  at  the  line  of 
contact  of  the  layers. 

(3)  Should  show  no  free  fatty  acids,  alkalies,  or  chlorides  when  tested  by  the  ordinary 
methods. 

(4)  If  10  Gm.  of  wool-fat  be  heated  with  50  Cc.  of  water  on  a  bath  of  boiling  water  until 


210  ANALYSIS   OF  DRUGS,   ETC. 

The  following  are  the  saponification  equivalents  of  the  oils  referred  to  : — 

Per  cent,  of  KHO  neutralized. 

Almond     ......  191  to  200 

Castor        ......  179  ,,  180 

Cod  liver 175  ,,  185 

Cotton       ......  191   „  196 

Croton 212  ,,  218 

Linseed     ......  187  ,,  195 

Olive 191  „  195 

Lard  oil     ......  195  ,,  197 

Cacao  butter      .....  188  ,,  195 

(4)  Specific  Heating  Power.     The  process  consists  in  placing  50  Gm.  of 
the  oil  or  melted  fat  in  a  glass  cylinder,  immersing  a  thermometer,  noting 
the  temperature,  and  then  causing  10  Cc.  of  strong  sulphuric  acid,  brought 
to  exactly  the  same  temperature  as  that  of  the  oil,  to  flow  slowly  in  from  a 
stoppered  burette,  stirring  with  the  thermometer  all  the  time,  and  noting  the 
extreme  point  to  which  the  mercury  rises.     The  experiment  is  then  repeated 
•under  exactly  the  same  conditions,  using  50  Cc.  of  distilled  water  instead  of  oil, 
and  the  rise  is  again  noted.     Lastly,  the  rise  in  temperature  observed  with 
the  oil  is  divided  by  that  shown  with  the  water.     The  stopper  of  the  burette 
should  be  so  set  that  it  takes  exactly  one  minute  to  deliver  10  Cc.  of  acid. 
The  following  are  some  characteristic  results  : — 

Water roo 

Castor 0-89  to  0-92 

Cod  liver 2-46  ,,  272 

Cotton '.  1-63  ,,  170 

Linseed 3-20  ,,  3-49 

Olive o  89  ,,  0-94 

The  rise  is  so  great  with  linseed  oil,  that  it  is  best  to  work  upon  it  after 
diluting  it  one  half  with  a  mineral  oil,  previously  found  to  give  only  a  slight 
definite  rise,  and  to  make  a  correction. 

(5)  Qualitative  Tests  for  U.S.P.  Fixed  Oils  and  Fats. 

(a)  Almond  oil.  (i)  Remains  clear  at — IO°C.,  and  does  not  congeal  until  cooled  to  nearly 
— 20°  C.  (absence  of  olive  oil  or  lard  oil}. 

(2)  2  Cc.  vigorously  shaken  with  I  Cc.  of  fuming  nitric  acid  and  I  Cc.  of  water  forms  a 
whitish  mixture,  which,  after  standing  for  some  hours  at  about  10°  C.  (50°  F.),  separates 
into  a  solid,  white  mass  and  a  slightly  colored  liquid  (distinction  from  oils  of  peach  and  apricot 
kernels,  which  give  a  red  color,  and  sesame  and  cotton  seed  oils,  which  are  colored  brown). 

(3)  10  Cc.  mixed  with  15  Cc.  of  solution  of  sodium  hydroxide  (i  in  6)  and  10  Cc.  of 
alcohol,  and  the  mixture  allowed  to  stand  at  a  temperature  of  35°  to  40°  C.,  with  occasional 
agitation,   until  it  becomes  clear,  and  then  diluted  with  100  Cc.  of  water,  yields  a  clear 
solution  which,  on  adding  an  excess  of  hydrochloric  acid,  will  throw  up  a  layer  of  oleic  acid. 
This,  when  separated  from  the  aqueous  liquid,  washed  with  warm  water,  and  clarified  by 
heating  on  a  water-bath,  will  remain -liquid  if  cooled  to  15°  C.     This  acid,  when  mixed  with 
an  equal  volume  of  alcohol,  should  yield  a  clear  solution,  which  at  15°  C.  should  not  deposit 
any  fatty  acids,  nor  become  turbid  upon  the  further  addition  of  I  volume  of  alcohol  (dis- 
tinction from  olive,  arachis,  cotton  seed,  sesame,  and  other  fixed  oils). 

(U)  Castor  oil.  (i)  Soluble  in  all  proportions  in  absolute  alcohol,  and  in  glacial  acetic 
acid,  and  in  3  times  its  volume  of  92*5  per  cent,  alcohol. 

(2)  3  Cc.  shaken  for  a  few  minutes  with  3  Cc.  of  carbon  disulphide  and  I  Cc.  of  sulphuric 
acid,  should  not  acquire  a  blackish-brown  color  (absence  Q{  foreign  oils). 

(c)  Cod  liver  oil.  (i)  Very  slightly  soluble  in  alcohol,  but  readily  soluble  in  ether, 
chloroform,  or  carbon  di^ulphide  ;  also  in  2-5  parts  of  acetic  ether. 

(2)  I   drop  of  the  oil  dissolved  in  20  drops  of  chloroform   and  shaken  with  I  drop  of 
sulphuric   acid,    will   give   a   violet-red    tint,    rapidly   changing   to    rose-red    and,    finally, 
brownish-yellow. 

(3)  If  a  glass  rod  moistened  with  sulphuric  acid  be  drawn  through  a  few  drops  of  the  oil, 
on  a  porcelain  plate,  a  violet  color  will  be  produced. 

(4)  If  two  or  3  drops  of  fuming  nitric  acid  be  allowed  to  flow  alongside  of  10  or  15  drops 
of  the  oil,  contained  in  a  watch-glass,  a  red  color  will  be  produced  at  the  point  of  contact. 
On  stining  the  mixture  with  a  glass  rod,  this  color  becomes  bright  rose-red,  soon  changing 
to  lemon-yellow  (distinction  from  seal  oil,  which  shows  at  first  no  change  of  color,  and  from 
other  fish  oils,  which  become  at  first  blue  and  afterwards  brown  and  yellow). 


ANALYSIS  OF  FIXED   OILS  AND  FATS.  211 

(d)  Cotton  seed  oil.  (i)  On  cooling  the  oil  to  a  temperature  below  12°  C.,  particles  of 
solid  fat  will  separate.  At  about  o°  to — 5°  C. ,  the  oil  becomes  nearly  or  quite  solid. 

(2)  6  Cc.  of  the  oil  thoroughly  shaken  for  ten  minutes  with  a  mixture  of  I  '5  Cc.  of  nitric 
acid  and  0*5  Cc.  of  water,  then  heated  in  a  bath  of  boiling  water  for  not  more  than  fifteen 
minutes,  will  assume  an  orange  or  reddish-brown  color,  and  will  form  a  semi-solid  mass  in 
twelve  hours  at  ordinary  temperature. 

(3)  5  Cc.  thoroughly  shaken  in  a  test-tube  with  5  Cc.  of  an  alcoholic  solution  of  silver 
nitrate  (cri  Gm.  of  silver  nitrate  in  10  Cc.  of  alcohol  and  2  drops  of  nitric  acid),  and  then 
heated  for  about  five  minutes  on  a  water-bath,  will  assume  a  red  or  reddish-brown  color. 

(4)  If  2  Cc.  be  mixed  in  a  test-tube  with  I  Cc.  each  of  amyl  alcohol  and  carbon  disulphide 
containing  i  per  cent,  of  sulphur  in  solution,  and  the  test-tube  be  immersed  to  one-third  or 
one-half  its  depth  in  boiling  salt  water,  a  red  color  will  develop  in  from  ten  to  fifteen 
minutes. 

(<?)  Croton  oil.  (i)  When  gently  heated  with  twice  its  volume  of  absolute  alcohol,  it 
forms  a  clear  solution  from  which  the  croton  oil  should  separate  on  cooling. 

(2)  If  2  Cc.  be  mixed  with  i  Cc.  of  fuming  nitric  acid  and  I  Cc.  of  water  and  then 
vigorously  shaken,  it  should  not  solidify,  even  partially,  after  standing  two  days  (absence  of 
other  non-drying  oils). 

(/)  Lard  oil.  (i)  At  a  temperature  a  little  below  10°  C.  (50°  F.),  it  usually  commences 
to  deposit  a  white,  granular  fat,  and  at  or  near  o°  C.  (32°  F.),  it  forms  a  solid  white  mass. 

(2)  Tested  for  the  presence  of  cotton  seed  oil,  as  above  directed  by  tests  (3)  and  (4),  none 
should  be  found. 

(3)  Should  be  completely  saponifiable  with  alcoholic  potassium  hydroxide  and  the  resulting 
soap  entirely  soluble  in  water,  without  separation  of  an  oily  layer  (absence  of  mineral  oils). 

(g)  Linseed  oil.  (i)  It  does  not  congeal  at  temperatures  above— 20°  C.,  and  is  soluble 
in  about  10  parts  of  absolute  alcohol,  and  in  all  proportions  in  ether,  chloroform,  petroleum 
benzin,  carbon  disulphide,  and  oil  of  turpentine. 

(2)  Should   be   completely   saponifiable   with   alcoholic    potassium   hydroxide,    and   the 
resulting  soap  entirely  soluble  in  water  without  leaving  an  oily  residue  (absence  of  mineral 
oils  and  rosin  oil). 

(3)  If  2  Cc.  of  the  oil  be  warmed  and  shaken  in  a  test-tube  with  an  equal  volume  of  glacial 
acetic  acid,  and  if  to  this  mixture,  after  cooling,  i  drop  of  sulphuric  acid  be  added,  a  greenish 
color  should  be  produced  (a  violet  color  under  these  circumstances  indicates  the  presence 
of  rosin  or  rosin  oils). 

(h)  Olive  oil.  (i)  When  cooled  to  from  8°  to  10°  C.,  the  oil  becomes  somewhat  cloudy 
from  the  separation  of  crystalline  particles,  and  at  o°  C.  it  forms  a  whitish  granular  mass. 

(2)  If  2  Cc.  of  olive  oil  be  shaken  vigorously  with  an  equal  volume  of  nitric  acid  (sp.  gr. 
1-37),  the  oil  should  retain  a  light  yellow  color,  not  becoming  orange  or  reddish-brown,  and 
after  standing  for  six  hours  should  change  into  a  yellowish-white  solid  mass  and  an  almost 
colorless  liquid  (absence  of  appreciable  quantities  of  cotton  seed  oil  zn.&  most  other  seed  oils). 

(3)  Tested  for  the  presence  of  cotton  seed  oil  by  the  tests  (3)  and  (4)  above  given,  none 
should  be  found. 

(4)  If  2  Cc.  of  the  oil  be  mixed  with  I  Cc.  of  hydrochloric  acid  (sp.  gr.  I'i8)  containing 
I  per  cent,  of  sugar,  and  the  mixture  be  shaken  for  half  a  minute  and  allowed  to  stand  for 
five  minutes,  and  then  3  Cc.  of  water  added  and  the  whole  again  shaken,  the  acid  layer 
shou'd  not  show  a  pink  color  (absence  of  sesame  oil). 

(1)  Cacao  butter  (theobromd).     (i)  Is  brittle  at  temperatures  below  I5°C.,  and  melts  at 
30°  to  35°  C.     It  is  readily  soluble  in  ether,  chloroform,  or  benzene  ;  also  soluble  in  100  parts 
of  cold  absolute  alcohol,  and  in  20  parts  of  boiling  absolute  alcohol ;  the  solutions  should  be 
neutral  to  test  paper. 

(2)  If  i  Gm.  of  oil  of  theobroma  be  dissolved  in  3  Cc.  of  ether  in  a  test-tube  at  a  tem- 
perature of  17°  C.,  and  the  tube  frequently  plunged  into  water  at  o°  C.,  the  liquid  should  not 
become  turbid  nor  deposit  white  flakes  in  less  than  three  minutes  ;  and  if  the  mixture  after 
congealing  be  again  brought  to  15°  C.,  it  should  gradually  form  a  perfectly  clear  liquid 
(absence  of  wax,  stearin,  tal/ow,  etc.). 

(/£)  Lard,  (i)  Specific  gravity  :  about  0-917  at  25°  C.,  and  about  0*904  at  40°  C.,  water 
at  25  C.  taken  as  the  standard.  It  melts  at  38°  to  40°  C.  to  a  perfectly  clear  liquid,  which 
is  colorless  in  thin  layers  and  from  which  an  aqueous  layer  should  not  separate. 

(2)  Tested  for  the  presence  of  cotton  s_jed  oil  as  above  (employing  tests  (3)  and  (4),  and 
applying  them  to  5  Cc.  of  melted  and  filtered  lard  while  still  warm),  none  should  be  found. 

(/)  Wool-fat,  (i)  Melts  at  about  40°  C.,  and  at  a  higher  temperature  vaporizes,  the 
vapor  igniting  and  burning  with  a  luminous,  sooty  flame. 

(2)  The  solution  of  wool-fat  in  chloroform  (i  in  50),  when  poured  upon  the  surface  of 
concentrated   sulphuric  acid,  gradually  develops  a  deep  brownish-red  color  at  the  line  of 
contact  of  the  layers. 

(3)  Should  show  no  free  fatty  acids,  alkalies,  or  chlorides  when  tested  by  the  ordinary 
methods. 

(4)  If  10  Gm.  of  wool-fat  be  heated  with  50  Cc.  of  water  on  a  bath  of  boiling  water  until 


2i4  ANALYSIS  OF  DRUGS,   ETC. 

formula,  in  which  A  =  per  cent,  of  apparent  cerotic  acid,  B  =*  per  cent,  of 
apparent  myricine,  X  =  unknown  cerotic  acid.     Then  — 
,   A  -X   .   ,       v    ,    B  -6-H7X 
' 


X  =  25-649  —  (-i6S9A  H-  '10738); 
or  for  Japan  wax  — 


Should  such  wax  also  contain  paraffin,  a  direct  estimation  thereof  must  also 
be  attempted.  This  may  usually  be  done  by  destroying  the  wax  on  the 
water  bath  with  fuming  sulphuric  acid,  and  then  cooling,  diluting,  extracting 
the  paraffin  with  ether  or  petroleum  spirit,  evaporating  off  the  solvent,  and 
weighing  the  paraffin.  It  is  to  be  noted  that  an  adulterant  containing  paraffin 
called  "  cerosin  "  is  now  produced,  which  sometimes  defeats  this  process. 

(/)  No  wax  containing  any  notable  amount  of  paraffin  ever  yields  percentage 
of  the  two  chief  ingredients  corning  up  to  100;  while  samples  adulterated 
with  fat  and  fatty  acids  (or  Japan  wax),  and  free  from  paraffin,  always  add 
up  to  a  figure  markedly  exceeding  103. 

(3)  B.P.  Standard  for  Beeswax.  5  grms.  of  the  beeswax,  melted  in  and 
mixed  with  boiling  alcohol  (90  per  cent.),  should  require  for  neutralisation 
not  less  than  r6  c.c.  of  normal  alcoholic  volumetric  solution  of  potassium 
hydroxide,  using  phenol-phthalein  as  an  indicator.  Upon  the  further  addition 
of  20  c.c.  of  the  volumetric  solution,  and  well  boiling  for  one  hour  under  a 
reflux  condenser,  not  less  than  6'2  nor  more  than  6*8  c.c.  should  be  found  to 
have  combined  with  the  beeswax,  as  shown  by  the  titration  of  the  uncombined 
alkali  with  volumetric  solution  of  sulphuric  acid.  If  5  grms.  of  beeswax  are 
heated  for  fifteen  minutes  with  25  grms.  of  sulphuric  acid  to  320°  F.  (160°  C.), 
and  the  mixture  diluted  with  water,  no  solid  waxlike  body  should  sep  irate 
(absence  of  paraffin).  Beeswax  should  not  yield  any  characteristic  reaction 
with  the  tests  for  starch. 

II.  Tests  to  distinguish  between  Chief  Unofficial  Waxes.    Dissolve,  by 
heat,  i  of  wax  in  10  of  chloroform,  and  cool  to  15°  C. 
Case  I.     The  cold  solution  is  clear. 

(1)  The  original  is  soluble  in  ether. 

(a)  Alcoholic  Fe^Cle  gives  ppt  insoluble  on  boiling  :  Myrica 

querdfolia. 

(b)  Alcoholic  Fe^Cl6  gives  black  :  Myrica  (species  uncertain). 

(c)  „  „          „     brown  colour,  but  no  ppt.  :    Oriziba 
wax. 

(L-)  The  original  is  not  entirely  soluble  in  ether. 

Saponify  by  boiling  with  10  parts  of  N  alcoholic  potash,  and  then 

boil  with  100  parts  H2O  :  — 
(a)  Completely  soluble  :  Japan  wax, 
(b}   Only  partially  soluble  :  African  beeswax. 
Case  II.  The  cold  chloroforrnic  solution  is  turbid. 

(T)  An  alcoholic  solution  of  the  original  becomes  turbid  with  alcoholic 
plumbic  acetate  :  Lac  wax. 

(2)  No  turbidity  is  produced;  then  — 

(a)  An  ethereal  solution  of  the  original  mixed  with   its  own 

volume  of  alcohol  becomes  turbid  :   Carnauba  wax. 
b    The  solution  is  clear  :  Bahia  wax. 


ANALYSIS  OF  ESSENTIAL    OILS. 


215 


XII.   ANALYSIS  OF   SOAP. 

(1)  Direct  Estimation   of  Fatty   Acids.      2   Gms.   of  the  soap,  in   fine 
shavings,   are  shaken  up  in  a  separator,  with  a  slight  excess  of  dilute  sul- 
phuric acid  to  liberate  the  acids.     Ether  is  then  added,  and  the  fatty  acids 
which  have  been  liberated  are  dissolved  up  in  it.     When  the  decomposition 
of  the  soap  is  complete,  the  liquid  below  the  ethereal  solution  is  removed. 
With  a  little  care  this  can  be  done  very  completely,   without  any   loss  of 
the  ethereal  solution.     The  ether  is  then  shaken  up  with  distilled  water,  and 
the   latter  drawn   off  as  before,  and  this  process  of  washing  repeated  three 
times  more.     When  all  but  a  few  drops  of  the  wash-water  have  been  drawn 
off,  a  few  drops  of  barium  chloride  solution  are  added,  the  mixture  shaken  up, 
and  the  last  traces  of  sulphuric  acid  thus  removed.     With  a  little  practice 
so   little    water   is  left  below  the  ethereal  solution  that   the  latter   can    be 
directly  drawn  off  and  evaporated  in  a  weighed  dish,  and  the  residue  finally 
dried  in  the  water  oven  and  weighed.     The  fatty  acids  thus  obtained  also  con- 
tain resin  acids  in  any  soap  made  from  fat  and  resin  (such  as  primrose  soap). 

(2)  Convenient  Method  for  General  Analysis,    (a)  Cut  the  soap  across,  and 
drop  on  the  fresh  surface  a  solution  of  phenol-phthalein  in  alcohol,  when  any 
red  color  shows  the  presence  of  free  alkali.     If  free  alkali  be  found,  dissolve 
5   Gms.  in  absolute  alcohol,  add  phenol-phthalein,  titrate  with  tenth-normal 
acid,  and  calculate  to  NaHO  or  KHO  according  to  which  alkali  is  present. 

(b)  Dissolve  2  Gms.  of  the  soap  in  absolute  alcohol  by  the  aid  of  heat, 
add  a  drop  of  solution  of  phenol-phthalein,  and  pass  CO2  till  any  red  color 
disappears.  Filter  through  a  tared  filter,  and  wash  any  insoluble  matter 
found  with  warm  alcohol,  dry  at  212°  F.  and  weigh,  which  will  give  Mai 
impurities  (such  as  alkaline  carbonates,  silicates,  or  borax).  The  filtrate  and 
washings  are  then  to  be  evaporated  on  the  water  bath  in  a  weighed  platinum 
dish,  the  residue  being  dried  in  the  water  oven  to  constant  weight  and 
weighed  =  actual  real  soap  present.  The  dish  and  contents  are  then  gently 
heated  to  redness,  the  residue  left  being  dissolved  in  water  and  titrated  with 
tenth-normal  acid,  using  methyl  orange  as  the  indicator.  The  number  of  Cc. 
used  is  multiplied  by  '0031  for  hard  soda  soaps,  or  by  '0047  f°r  s°ft  potash 
soaps,  and  the  resulting  amount  of  alkali  being  deducted  from  the  weight  of 
real  soap  found  the  difference  x  1*03  =  amount  of  fatty  acids.  The  weights 
of  real  soap  and  total  impurities  added  together,  and  deducted  from  2,  gives  the 
water  present  in  the  sample.  Finally,  everything  is  calculated  to  percentage. 

XIII.  ANALYSIS  OF  ESSENTIAL  OILS, 

i.  Physical  Constants.  The  specific  gravity  and  the  rotation  in  the 
polariscope,  using  a  tube  100  Mm.  long  at  a  temperature  of  25°  C.,  are  of 
importance,  although  variable  within  narrow  limits.  The  following  are  the 
average  results  with  the  U.S.P.  oils  : — 

Sp.  Gr.  at  25°  C.  Optical  Rotation  in  100  Mm.  tube  at  25°  C 

(if  F.).  (77°  F.). 

inactive. 

-2°. 

+  95°  (not  less), 
inactive. 

—  2°  (not  more). 
+  70°  to  +  80°. 

inactive  or  slightly  — . 

—  5°  (not  more), 
practically  inactive  ( —  or  +  1°. 
not  constant. 

+  7°  to  +  14°. 

—  25°  to  —  40°. 
+  50°  (about). 

+  10°  (not  more). 


Oleum  Amygdalae  Amarae 

I  '045  to  ro6o 

Anisi 

'975 

•985 

Aurantii    . 

•842 

•846 

Betulae 

1-172 

ri8o 

Cajuputi  . 

•915 

•925 

Cari 

'90S 

•915 

Caryophylli 

ro4o 

ro6o 

Chenopodii 

•965 

•989 

Cinnamoni 

i  '045 

i'055 

Copaibce  . 

•895 

•905 

Coriandri. 

•863 

•878 

Cubebae    . 

'90S 

•925 

Krigerontis 

•845 

•865 

,       Eucalypti  . 

'90S 

•925 

216 


ANALYSIS  OF  DRUGS,   ETC. 


Sp.  Gr.  at  25°  C. 

Optical  Rotation  in  100  Mm.  tube  at  25°  C. 

(77°  F.). 

(77°  F.). 

Oleum  Foeniculi  . 

'953  to    '973 

.     not  constant. 

,,      Gaultheriae 

1-172      ri8o 

—  i°  (not  more). 

,,      Hedeomas 

•920        -935 

.      +  18°  to  +  22°. 

„      Juniper!    . 
,,      Lavandulae 

•860        -880 
•880        -892 

.     not  constant,  dependent  on  age. 

,,      Limonis    . 

•851        -855 

.      +  60°  (not  less).     The  first  10  per  cent. 

1 

Menthse  piperitae 

.     -894 

•914    • 

-  25°  to  -  33°. 

> 

,,        viridis. 

*     -914 

'934    • 

-  35°  to  -  48°. 

Myristicae 

.     -862 

-910    . 

+  14°  to  +  28°. 

t 

Pimentse  . 

•  i  '033 

1-048    . 

not  constant,  gener; 

( 

Rosse 

.     -855 

•865    . 

»»                    5>                              >t 

! 

Rosmarini 

•     '894 

•912    . 

+  15°  (not  more). 

> 

Sabinae 

•     -903 

•923    . 

+  40°  to  +  60°. 

Santali 

.     -965 

'975    • 

-  1  6°  (not  less). 

J 

Sassafras  . 

.  1-065 

1-075    • 

+  4°  (not  more). 

> 

Sinapis      .         . 

.  1-013 

i  -020    . 

inactive. 

Terebinthinae    . 

.     -860 

,    -870    . 

not    constant,    but 

dextrogyrate. 

), 

Thymi      . 

.     -900  , 

.    '930    - 

—  3°  (not  more). 

of  oil  obtained  by  fractional  dis- 
tillation should  not  differ  more 
than  2°  from  the  original. 


American    oil    is 


The  boiling  point  is  scarcely  ever  constant,  as  these  oils  are  always  mixtures, 
and  therefore  require  fractional  distillation  in  a  proper  dephlegmator.  The 
results  depend  so  much  on  the  apparatus  employed,  that  it  is  hopeless  to  get 
any  agreement  in  this  respect  between  different  operators,  until  an  official 
method  is  definitely  laid  down.  If,  however,  50  Cc.  of  the  oil  be  distilled 
from  a  long-necked  Erlenmeyer  flask  of  100  Cc.  capacity,  with  a  thermometer 
in  the  neck,  and  placed  on  a  piece  of  wire  gauze,  to  which  heat  is  directly 
applied  by  a  Bunsen  burner,  fairly  concordant  estimations  may  be  made  on 
successive  quantities.  Treated  in  this  way  Oleum  Terebinthince,  U.S. P.  should 
practically  entirely  distil  over  between  155°  and  162°  C. 

The  combination  of  fractional  distillation  and  specific  gravity  or  optical 
rotation  is  often  very  useful  in  detecting  mixtures  of  essential  oils  with 
turpentine,  etc.  This  method  is  employed  by  the  U.S. P.  in  the  examination 
of  certain  oils  as  follows : — 

Oleum  Limonis  and  Oleum  Rosmarini  should  respectively  rotate  the  plane  of  a  ray  of 
polarized  light  not  les?  than  60°  and  not  more  than  15°  to  the  right  in  a  tube  100  millimeters 
long;  and  if  100  volumes  be  fractionally  distilled,  the  10  volumes  first  collected  should  not 
produce  a  rotation  differing  by  more  than  2°  from  that  produced  by  the  original  oil  in  the 
former  case,  and  should  also  be  dextrogyrate  in  the  latter. 

Oleum  Sinapis  Volatile  should  distil  between  148°  C.  and  152°  C.,  and  the  first  and  last 
portions  of  the  distillate  should  have  the  same  specific  gravity  as  the  original  oil  (absence  of 
ethylic  alcohol  and  petroleum). 

In  the  case  of  Oleum  Aurantii  Cortex  fractional  distillation  is  resorted  to,  and  any  oil 
passing  over  under  170°  C.  may  be  limonene,  but,  should  the  oil  be  adulterated  with 
turpentine,  pinene  may  also  come  over,  and  therefore  the  U.S. P.  applies  the  following  test 
to  this  fraction  :  — 

Dissolve  5  Cc.  of  the  fraction  to  be  tested  in  half  its  volume  of  glacial  acetic  acid,  add 
5  Cc.  of  amyl  nitrite,  cool  thoroughly  in  a  freezing  mixture,  and  add,  very  gradually,  5  Cc. 
of  a  mixture  of  equal  volumes  of  hydrochloric  acid  and  glacial  acetic  acid.  Collect  any 
crystals  which  separate  upon  standing,  on  a  force  filter,  and  wash  them  with  a  little  alcohol. 
Transfer  the  crystals  to  a  flask,  add  5  Cc.  of  £  alcoholic  KHO,  and  heat  on  a  water-bath 
fifteen  minutes.  Pour  into  cold  water,  collect  the  precipitate,  and  wash  it  with  cold  water. 
Recrystallize  the  dried  precipitate  from  alcohol,  and  determine  the  melting  point  of  the 
crystals.  Nitrosopinene  melts  at  132°  C.,  whereas  nitrosolimonene  melts  at  72°  C. 

The  determination  of  the  congealing  or  crystallizing  point  of  an  oil  is  also 
occasionally  of  value.  This  method  is  applied  to  the  following  oils  by  the 
U.S. P.  as  under  : — 

Oleum  Anisi.  Transfer  10  Cc.  of  the  oil  to  a  test-tube  placed  in  water  cooled  by  ice  ; 
insert  a  thermometer  at  once  into  the  oil,  and  allow  it  to  remain  undisturbed  until  its 


ANALYSIS  OF  ESSENTIAL    OILS. 


217 


temperature  has  fallen  to  about  6°  C.  Induce  crystallization  either  by  rubbing  the  inner 
wall  of  the  test-tube  with  the  thermometer  or  by  the  addition  of  a  particle  of  solid  anethol, 
and  stir  continuously  during  the  solidification  of  the  oil.  The  highest  temperature  reached 
during  the  crystallization  is  regarded  as  the  congealing  point,  and  this  should  not  be 
below  15°  C. 

Oleum  Fceniculi.     Is  similarly  done,  but  a  freezing  mixture  must  be  used  to  bring  the 
temperature  down  to  — 5°  C.,  and  the  congealing  point  should  not  be  below  5°  C. 
Oleum  Rosa  should  congeal  between  18°  and  22°  C.  when  tested  as  follows : — 
Introduce  about    10  Cc.    of  oil    into   a  test-tube  of  about  15  Mm.  diameter;   insert   a 
thermometer  so  that  it  touches  neither  the  bottom  nor  the  sides  of  the  tube.     Raise  the 
temperature  of  the  oil  in  the  tube  from  4°  to  5°  above  the  saturation  point  by  grasping  it  in 
the  hand,  and  shake  the  tube  gently.     Allow  the  oil  to  cool,  and  when  the  first  crystals 
appear,   note  the  temperature.     This  is  regarded  as  the  congealing  point ;  a  second  test 
should  be  made  for  confirmation. 

2.  Solubility.      The   presence   of  turpentine   and   various  adulterants  is 
frequently  made  manifest  by  the  use  of  a  definite  volume  of  alcohol,  and  on 
this  point  the  U.S.P.  lays  down  the  following  standards :  — 

Name.  Standard  of  Solubility. 

Oleum  Amygd.  Amane equal  vols.  of  70  per  cent,  alcohol. 

Anisi 5  ,,9° 

Cajuputi I  ,,      80 

Cari equal  ,,      92*3 

Caryophylli          .         .         .          .          .2  ,,       70 

Chenopodii          .         .         .         .         .5  ,,70 

Cinnamoni 2  »       7° 

Copaike      ......     2  ,,      92-3 

Coriandri 3  ,,70 

Eucalypti 3  ,,70 

Fceniculi     .         .         .         .         .         .   10 (or less)  ,,      80 

Hedeomae 2  ,,70 

Juniperi       ......   10  ,}      90 

Lavandulse.         .....     3  »      7° 

Menthae  piperitse          .         .         .         .4  ,,70 

,,        viridis    .....     equal  ,,      80 

Myristicse    ,         .         .         .         .         .3  ,,      90 

3.  Chemical  Analysis.     Qualitative  tests  are,  as  a  rule,  unnecessary,  because 
each  oil  has  a  perfectly  characteristic  odor,  but  some  are  useful   to  detect 
impurities,  such  as  :— 

(a)  Alcohol  in  essential  oils  may  be  detected  by  shaking  up  a  measured 
quantity  with  water  in  a  burette,  when  the  bulk  will  diminish  owing  to  the 
alcohol  dissolving  out. 

(b)  Metals  (chiefly  copper  and  lead)  are  detected  by  shaking  up  the  oil  with 
a  little  very  dilute  acid,  and  then  applying  the  usual  tests  to  the  acid  liquid. 

(c)  Petroleum  products  are  detected  by  the  action  of  sulphuric  acid,  which 
will  combine  with  the  oil,  but  not  with  paraffins.     The  U.S.P.  applies  this 
method  to  the  detection  of  petroleum  in  oil  of  turpentine  as  follows  : — 

If  5  Cc.  of  oil  of  turpentine  be  placed  in  a  small  beaker,  and  20  Cc.  of  sulphuric  acid  be 
gradually  added,  with  agitation,  while  the  beaker  is  cooled  by  immersion  in  cold  water,  and 
the  contents,  after  cooling  and  renewed  agitation,  be  transferred  to  a  burette,  graduated  in 
tenths,  the  clear  layer  which  forms  after  the  dark  mass  has  settled  should  not  measure  more 
than  o-35  Cc.  (absence  of  petroleum,  benzzn,  kerosene,  or  similar  hydrocarbons). 

Quantitative  Analysis  to  ascertain  the  amount  of  the  active  odoriferous 
principle  is  now  being  more  and  more  applied  to  essential  oils.  When  these 
active  constituents  are  not  simple  mixtures  of  terpenes,  they  are  capable  of 
chemical  determination,  and  may  be  divided  into  six  classes  as  follows  :  — 
(a)  Esters  (compound  ethers) ;  (b)  Phenols  or  phenolic  ethers ;  (c)  Aldehyds  ; 
(d)  Ketones;  (e)  Alcohols;  (/)  Isothiocyanates.  They  may  be  respectively 
tested  for  and  estimated  as  follows  : — 

(a)  Estimation  of  Esters  (compound  ethers).  These  bodies  are  capable  of 
sapomncation  by  boiling  with  §  alcoholic  KHO,  and  the  amount  of  alkali 
unconsumed  having  been  ascertained  by  residual  titration  with  £  acid,  the 


2i 8  ANALYSIS  OF  DRUGS,   ETC. 

difference  gives  the  means  of  calculating  the  amount  of  ester.  Taking,  for 
example,  bornyl  acetate  (existing  in  OL  Ros?narini\  the  equation  would  be : — 

C10HJ7O .  C2H3O  +  KHO  =  C10H17 .  HO  +  KC.H3O,, 

and  therefore  each  Cc.  of  \  KHO  consumed  would  equal  '09734  bornyl 
acetate.  For  the  menthyl  acetate  (in  Ol.  Menth.  pip.)  the  similar  equivalent 
would  be  '09834.  The  U.S. P.  directions  are  : — 

Introduce  10  Cc.  of  oil  into  a  tared  flask,  and  note  the  exact  weight ;  add  25  Cc.  of 
£  alcoholic  KHO,  connect  with  a  reflux  condenser,  and  boil  the  mixture  during  one  hour. 
After  cooling  titrate  the  residual  alkali  with  £  HJ5O4,  using  phenol-phthalein  as  indicator. 
Subtract  the  number  of  Cc.  of  £  H2SO4  required  from  the  25  Cc.  of  £  KHO  taken,  multiply 
the  difference  by  9734  (or  9*834),  and  divide  the  product  by  the  weight  of  the  oil  taken  to 
find  the  percentage. 

Ol.  Rosmarini  should  contain  not  less  than  5  per  cent.,  and  OL  Menth. 
pip.  not  less  than  8  per  cent.,  of  their  respective  esters.  The  esters  in  Ol. 
Roses  not  having  as  yet  been  properly  studied,  the  U.S. P.  takes  an  empirical 
saponification  factor  founded  on  experience,  thus  :— 

Place  about  2  Cc.  of  the  oil  in  a  weighing-bottle,  and  weigh  accurately.  Transfer  it,  with 
the  aid  of  a  little  alcohol,  to  a  100  Cc.  flask,  and  add  20  Cc.  of  £  alcoholic  KHO.  Connect 
the  flask  with  a  reflux  condenser,  and  boil  the  mixture  during  thirty  minutes  on  a  water-bath. 
When  cool,  add  50  Cc.  of  distilled  water  and  a  few  drops  of  phenol-phthalein,  and  titrate 
with  £  H2SO4.  Subtract  the  number  of  Cc.  of  £  H2SO4  required,  from  20,  multiply  the 
difference  by  27^87,  and  divide  by  the  weight  of  the  oil  to  obtain  the  saponification  value, 
which  should  be  between  10  and  17. 

(b)  Estimation   of  Phenols   and  Phenolic  Ethers.     Such  bodies  are  met 
with    in    anethol    CsH5 .  CeH4 .  OCH3     (in     oil     of    anise)    and    eugenol 
C6H3 .  OCH3 .  OH  .  C3H5  (in  oils  of  clove,  pimento,  etc.).     The  U.S.P.  does 
not  make  any  estimation  of  the  former,  relying  on  the  other  constants  for  OL 
Anisi,  especially  the  congealing  point  (see  supra),  but  it  assays  the  oils  of 
clove,  pimento,  and  thyme  for  the  latter  by  taking  advantage  of  the  fact  that 
such  bodies  combine  with  and  dissolve  in  solutions  of  alkaline  hydroxides, 
and  can  be  so  extracted  from  a  bulk  of  oil,  and  the  unacted-upon  portion 
read  off  thus  : — 

Introduce  into  a  flask  with  a  long  neck  (graduated  in  tenths)  10  Cc.  of  the  oil  of  pimenta 
and  loo  Cc.  of  5  per  cent,  solution  of  KHO,  and  shake  the  mixture  for  five  minutes.  When 
the  liquids  have  separated  completely,  add  sufficient  KHO  solution  to  raise  the  lower  limit 
of  the  oily  layer  to  the  zero  mark  of  the  scale,  and  note  the  volume  of  residual  liquid. 

This  should  not  exceed  2  Cc.,  3*5  Cc.,  and  8  Cc.  respectively  in  oils  of 
clove,  pimento,  and  thyme,  thus  proving  them  to  contain  respectively  80,  65, 
and  20  per  cent,  of  phenolic  bodies. 

(c)  Estimation  of  Aldehyds.     Such  bodies  are  met  with  as  cinnamic  aldehyd 
C6H5.C2H2.  CHO  (in  oils  of  cinnamon  and  cassia),  benzoic  aldehyd  (in  oil 
of  bitter  almonds),  citral  CioHi6O  (in  oil  of  lemon),  etc.,  and  to  estimate  them 
advantage  is  taken  of  the  well-known  reaction  of  aldehyds  with  sodium  or 
potassium  bisulphite,  whereby  a  crystalline  compound  is  produced  which  is 
soluble  in  water,  and  thus  the  aldehyd  can  be  removed  and  the  rest  of  the 
oil  left  and  measured.     The  U.S.P.  directs  for  OL  Cinnamoni :— 

Introduce  into  a  flask  with  a  long  graduated  neck  (in  5V  Cc.),  by  means  of  a  measuring- 
pipette,  10  Cc.  of  the  oil  of  cinnamon,  add  IO  Cc.  of  a  30  per  cent,  solution  of  sodium 
Bisulphite,  shake  the  flask,  and  heat  it  in  a  water-bath  containing  boiling  water  until  the 
contents  are  liquefied;  add  successive  portions  (10  Cc.  each)  of  the  bisulphite  solution, 
shaking  and  heating  as  before,  after  each  addition,  until  the  flask  is  three-fourths  filled. 
Continue  to  heat  it  in  the  water-bath  until  the  odor  of  cinnamic  aldehyd  is  no  longer  per- 
ceptible, cool  the  flask  to  about  25°  C.,  and  add  enough  of  the  bisulphite  solution  to  raise 
the  lower  limit  of  the  oily  layer  to  the  zero  mark  of  the  scale.  The  residual  liquid  should 
not  measure  more  than  2 '5  Cc.,  corresponding  to  at  least  75  per  cent.,  by  volume,  of 
cinnamic  aldehyd. 

For  the  estimation  of  benzaldehyd  in  OL  Amygd.  Amarcz,  and  of  citral  in 


ANALYSIS   OF  ESSENTIAL    OILS.  219 

OL  Limonis,  this  rough  process  is  not  sufficiently  delicate,  therefore  the  U.S. P. 
directs  as  follows  : — 

(1)  Benzaldehyd.     Introduce  into  a  tared  150  Cc.  flask  10  Cc.  of  purified  kerosene,  note 
the  exact  weight,  add  12  drops  of  the  oil,  and  again  note  the  weight;  add  20  Cc.  of  dis- 
tilled water  with  6  drops  of  phenol-phthalein,  and  then  neutralize  the  solution  exactly  by 
the  addition  of  ^  NaHO,  agitating  the  flask  thoroughly.     Add  from  a  burette,  gradually, 
a  solution  of  sodium  sulphite  (i  in  5),  alternating  with  £  HC1  from  ^  second  burette,  until 
10  Cc.  of  the  sodium  sulphite  solution  have  been  added,  and  enough  £  HC1  to  maintain  the 
neutrality  of  the  mixture  ;  after  adding  a  few  drops  of  phenol-phthalein,  and  agitating  the 
flask  frequently,  allow  it  to  stand  two  hours  to  insure  a  permanent  condition  of  neutrality,  and 
then  note  the  number  of  Cc.  of  the  £  HC1  used.     Carry  out  a  blank  test,  identical  with  the 
foregoing,  without  the  oil,  and  note  the  amount  of  ^  HC1  consumed.     Subtract  the  number 
of  Cc.  required  in  the  blank  test  from  the  number  required  in  the  original  test ;  each  Cc.  of  this 
difference  corresponds  to  0-0526  Gm.  of  benzaldehyd.     To  find  the  percentage,  multiply  the 
above  difference  by  0-0526,  and  this  product  by  100,  and  divide  by  the  weight  of  the  oil  taken. 

This  process  is  also  applicable  to  the  assay  of  artificial  benzaldehyd,  which 
should  show  84  per  cent.,  while  the  natural  Ol.  Amygd.  Am.  should  contain 
85  per  cent.  The  same  process  is  also  applicable  to  artificial  cinnamic 
aldehyd,  except  that  the  equivalent  for  each  Cc.  ^  HC1  is  0*033,  and  the 
article  should  show  95  per  cent. 

(2)  Citral.     Introduce  about  15  Cc.  of  oil  of  lemon  into  a  counterpoised  150  Cc.  flask,  and 
note  the  exact  weight ;  add  5  Cc.  of  distilled  water  and  a  few  drops  of  phenol-phthalein,  and 
then  neutralize  the  liquid  exactly  by  the  cautious  addition  of  ^  NaHO.     Add  25  Cc.  of  a 
neutral  solution  of  sodium  sulphite  (i  in  5),  and  immerse  the  flask  in  a  water-bath  containing 
boiling  water.     From  a  burette  add,  as  needed,  just  sufficient  £  HC1  to  maintain  the  neutrality 
of  the  mixture,  keeping  the  flask  continuously  heated  and  frequently  agitated,  and  adding  a 
drop  or  two  of  phenol-phthaleiri.     When  a  permanent  condition  of  neutrality  is  reached,  note 
the  number  of  Cc.  of  the  £  HC1  consumed.     Carry  out  a  blank  test,  identical  with  the  tore- 
going,  without  the  oil,  and  note  the  amount  of  £  HC1  consumed.     Subtract  the  number  of 
Cc.  required  in  the  blank  test  from  the  number  required  in  the  original  test ;  each  Cc.  of  this 
difference  corresponds  to  0-03802  Gm.  of  citral.     To  find  the  percentage,  multiply  the  above 
difference  by  0*03802,  and  this  product  by  100,  and  divide  by  the  weight  of  the  oil  of  lemon 
taken.     The  oil  should  not  show  less  than  4  per  cent. 

(d)  Estimation  of  Ketones  or  organic  oxides.     These  bodies,  such  as  carvol 
(in  oils  of  carraway,  dill,  and  green  mint)  and  cineol  (in  oils  of  cajuput  and 
eucalyptus),   combine   with  phosphoric  acid  to  form  a  precipitate   which  is 
insoluble,  but  is  decomposed  by  the  action  of  warm  water.     The  U.S. P.  only 
employs  the  process  for  cineol,  and  directs  as  follows : — 

Introduce  into  a  beaker  a  solution  prepared  by  dissolving  10  Cc.  of  oil  in  50  Cc.  of  purified 
petroleum  benzin  ;  immerse  the  beaker  in  a  freezing  mixture  and  add  phosphoric  acid,  drop 
by  drop,  with  constant  stirring,  until  the  white  magma  of  cineol  phosphate  formed  begins  to 
assume  a  yellowish  or  pinkish  tint ;  then  transfer  the  magma  to  a  force  filter,  wash  it  with 
cold  purified  petroleum  benzin,  and  then  dry  it  by  pressure  between  two  porous  plates. 
Transfer  the  precipitate  to  a  narrow  graduated  cylinder,  and  add  warm  water,  which  will 
cause  separation  of  the  cineol.  The  volume,  in  Cc.,  of  the  separated  oil,  multiplied  by  10, 
represents  the  volume  per  cent,  of  cineol.  Thus  tested,  01.  Cajuputi  should  show  55  per  cent., 
and  Ol.  Eucalypti  50  per  cent. 

(e)  Estimation  of  alcoholic  bodies.     These  bodies,  such  as  borneol  CioHigO 
(in   oil  of  rosemary),   menthol  CioH2oO  (in  oil  of  peppermint),  and  santalol 
CisHgcO  (in  santal  oil),  may  all  be  estimated  by  first  converting  them  into 
their  acetic  ester,  and  then  titrating  that  as  already  directed  under   Esters 
(see  (a)  supra).     The  following  is  the  method  of  acetylization  : — 

Introduce  10  Cc.  of  the  oil  into  a  flask  provided  with  a  ground-glass  tube-condenser 
(acetylization  flask),  add  10  Cc.  of  acetic  acid  anhydride  and  about  I  Gm.  of  anhydrous 
sodium  acetate,  and  boil  gently  during  one  hour.  Allow  it  to  cool,  wash  the  acetylized  oil  with 
distilled  water,  and  afterwards  with  5  per  cent,  solution  of  NaHO.  until  the  mixture  is  slightly- 
alkaline  to  phenol-phthalein,  and  then  dry  it  with  the  aid  of  fused  calcium  chloride,  and  filler. 

In  dealing  with  Ol.  Santali  this  process  is  applied  directly,  but  in  the  oils 
of  rosemary  and  peppermint  it  is  performed  on  the  residual  oil  left  after  esti- 
mation of  the  respective  esters  in  10  Cc.  of  the  original  oil  (see  (a)  supra). 


220 


ANALYSIS  OF  DRUGS,   E1C. 


Having  thus  obtained  the  acetic  ester,  we  then  proceed  to  estimate  it  by 
residual  titration.     For  santal  oil  the  U.S.P.  instructs  as  follows : — 

Transfer  to  a  tared  100  Cc.  flask  3  Cc.  of  the  dry  acetylized  oil,  note  the  exact  weight,  add 
50  Cc.  of  £  alcoholic  KHO,  connect  with  a  reflux  condenser,  and  boil  gently  during  one 
hour.  After  cooling,  titrate  the  residual  alkali  with  £  H2SO4,  using  phenol-phthalein  as 
indicator.  Subtract  the  number  of  Cc.  of  £  H2SO,  required  from  the  50  Cc.  of  £  alcoholic 
KHO  taken,  multiply  the  difference  by  1 1  -026,  and  divide  by  the  weight  of  the  dry  acetylized 
oil  taken,  less  the  above  difference  multiplied  by  0*021  ;  the  quotient  will  represent  the 
percentage  of  santalol  in  the  oil  of  santal,  which  should  amount  to  90  per  cent. 


ANALYSIS  OF  ESSENTIAL    OILS. 


221 


/4  —      2&r«*f«, 

2  -.   •&^<nf«*t- 


For  Ol.  Menth.  pip.  the  U.S. P.  directs  to  take  5  Cc.  of  the  acetylized  oil 
and  then  proceed  exactly  as  above,  except  that  the  difference  is  to  be 
multiplied  by  7749,  and  the  product  divided  by  the  weight  taken,  less  the 
above  difference  multiplied  by  0*021  ;  the  quotient  will  represent  the  per- 
centage of  menthol  in  the  oil  of  peppermint. 

For  OL  Rosmarini  the  procedure  is  the  same  as  for  peppermint,  except 
that  the  two  factors  are  7*649  and  0*021  respectively. 

It  will  be  observed  that  the  oils  of  peppermint  and  rosemary  are  doubly 


222  ANALYSIS  OF  DRUGS,   ETC. 

assayed,  and  the  standards  are  respectively  not  less  that  8  of  menthyl  acetate 
and  50  of  total  (menthol  +  menthyl  acetate),  and  5  of  bornyl  acetate  and 
15  of  total  (borneol  4-  bornyl  acetate). 

(f)  Estimation  of  Allyl  isothiocyanate.  P'or  the  assay  of  volatile  oil  of 
mustard,  the  U.S. P.  employs  combination  with  silver  and  residual  titration 
as  follows : — 

Weigh  accurately  about  2  Gm.  of  volatile  oil  of  mustard,  and  dilute  this  with  sufficient 
alcohol  to  make  50  Cc.  of  the  solution  represent  I  Gm.  of  the  oil ;  of  this  solution,  5  Cc.  are 
transferred  to  a  100  Cc.  measuring  flask,  and  30  Cc.  of  ^  AqNO3  and  5  Cc.  of  ammonia 
water  are  added.  The  flask  is  well-stoppered  and  set  aside  in  a  dark  place  for  twenty-four 
hours.  The  contents  of  the  flask  are  diluted  with  water  to  the  100  Cc.  mark  and  filtered. 
To  50  Cc.  of  the  filtrate,  4  Cc.  of  nitric  acid  and  a  few  drops  of  ferric  ammonium  sulpuate 
are  added,  and  finally  sufficient  ^  KCNS  to  produce  a  permanent  red  color ;  not  more  than 
5*6  Cc.  of  the  latter  reagent  should  be  required  (each  Cc.  of  ^  AqNOg  consumed  corre- 
sponding to  o '00492  gramme  of  allyl  isothiocyanate). 

DIVISION   II.     ANALYSIS    OF    URINE. 

A  sample  of  urine  taken  for  analysis  should  be  that  first  passed  by  the 
patient  in  the  morning,  or,  better,  a  portion  taken  from  the  total  twenty-four 
hours'  urine. 

The  following  are  the  chief  points  on  which  information  is  usually  required 
by  the  physician  who  submits  urine  for  examination  to  an  analyst  :— 

1.  Take  the  specific  gravity,  which  should  range  from   roi5  to   1-025  at 
60°  F.     For  every  i°  F.  above  60°  add  'oooi  to  the  observed  specific  gravity. 
By  multiplying  the  last  two  decimals  of  specific  gravity  by  2*33  we  have  the 
grammes  per  litre  of  total   solid  matter.      Make,   a  note  also    of  the    daily 
quantity,  which  should  be   1200  to  1500  c.c.  (40 — 50  fl.  oz.).     On  standing 
some  time  urine  undergoes  ammonic  fermentation,  and  becomes  alkaline  in 
reaction. 

Note. — In  diabetes  the  gravity  is  too  high,  sometimes  reaching  1*060,  while  in  albuminuria 
it  is  abnormally  low,  even  occasionally  falling  to  I  '005. 

2.  Examine  the  reaction,  which  should  be  very  faintly  acid. 

3.  Set  a  portion  to  settle  in  a  long  glass,  and  examine  the  deposit  under 
the  microscope   for  calcium   oxalate  or  phosphate,  uric  acid  or  urates,  pus, 
casts  or  kidney  tubes,  etc.,  etc.     (See  pages  212  and  213,  and  fig.  50,  p.  218.) 

Note. — The  nature  of  the  deposit  may  also  be  confirmed  chemically  as  follows  : — 

(a)  Warm  the  urine  containing  the  sediment,  when,  if  the  latter  should  dissolve,  it 
consists  entirely  of  urates.  In  this  case  let  it  once  more  crystallise  out,  and 
examine  it  by  the  ordinary  course  for  Ca,  Na,  and  NH4,  to  ascertain  the 
bases. 

(J>)  If  the  deposit  be  not  dissolved  by  heating,  let  it  settle,  wash  once  by  decantation 
with  cold  water,  and  warm  with  acetic  acid.  Phosphates  will  dissolve,  and 
may  be  reprecipitatecl  from  the  solution  by  excess  of  NII4HO  filtered  out, 
well  washed  with  boiling  H2O,  dissolved  in  HC2H3O.>,  and  examined  for  Ca 
or  Mg  by  the  usual  course  for  these  metals  in  presence  of  PO4. 

(c)  If  the  deposit  be  insoluble  in  acetic  acid,  warm  it  with   HC1.      Any  soluble 

portion  is  calcium  oxalate,  which  may  be  precipitated  by  NH4HO. 

(d)  If  the  deposit  be  insoluble  in  HC1,  it  is  probably  uric  acid.     In  this  case  apply 

the  murexid  test  as  follows  : — Place  it  in  a  small  white  dish,  remove  moi  ture 
by  means  of  a  piece  of  bibulous  paper,  add  a  drop  or  two  of  strong  HNO3, 
and  evaporate  to  dry  ness  at  a  gentle  heat.  When  cold  add  a  drop  of 
NH4HO,  which  will  produce  a  purple  colour,  deepened  to  violet  by  a  drop 
of  KHO. 

4.  Test  for  albumin,  as  follows  : — 

(a)  Boiling  test.     Filter  the  urine,  place  10  c.c.  in  a  narrow  test  tube, 
and  add  one  drop  of  acetic  or   nitric  acid.      Heat  the  tube 


ANALYSIS  OF  URINE. 


221 


over  a  small  flame  in  such  a  way  that  the  upper  portion  of 
the  liquid  only  shall  be  heated.  Coagulation  will  take  place, 
and  the  presence  of  albumin  will  be  evident  from  the  formation 
of  a  turbidity  ranging  from  a  faint  cloud  to  a  dense  coagulum, 
but  always  strongly  contrasted  with  the  clear  liquid  beneath, 
which  was  not  heated.  Mucin  also  precipitates  with  this  test. 

(£)  Nifric  test.  To  five  volumes  of  cold  saturated  solution  of  magnesium 
sulphate  add  one  volume  of  nitric  acid  (sp.  gr.  1*42),  and  pre- 
serve this  reagent  for  use.  Pour  some  perfectly  clear  filtered 
urine  into  a  tube,  and  carefully  add  an  equal  volume  of  the 
reagent,  delivered  gently  from  a  pipette,  so  that  the 
liquids  shall  not  mix.  An  opalescent  zone  will 
form  at  the  point  of  contact  either  immediately  or 
within  twenty  minutes,  according  to  the  quantity 
of  albumin  present.  This  zone  should  not  dissolve 
on  gently  warming,  but  should  be  a  distinct  ring 
at  the  bottom  of  the  urine,  and  not  a  general  haze 
near  the  top,  which  latter  indicates  mutin.  If  the 
zone  of  contact  has  a  pink  colour,  indican  or  other 
colouring  matter  is  excessive.  Indican  may  be 
further  confirmed  by  mixing  equal  volumes  of 
urine,  strong  HC1,  and  chlorine  water,  which  pro- 
duces a  violet  colour,  and  may  be  estimated  by 
colour  titration  with  chloroformic  solution  of  indigo 
of  known  strength. 

(c]  Picric  acid   test.     Dissolve   7*5   grms.  of  pure    crys- 

tallised trinitro-phenol  (picric  acid)  in  500  c.c.  of 
water,  let  it  stand  for  some  days  to  perfectly 
clarify,  pour  oft",  and  preserve  the  reagent  for  use. 
Mix  some  of  the  filtered  urine  in  a  tube  with  an 
equal  volume  of  this  reagent,  look  for  any  cloud 
or  precipitate,  and  then  heat  to  boiling.  The  true 
albumin  cloud  will  remain  permanent,  while  that 
due  to  peptones  or  alkaloids  accidentally  present 
will  be  dissolved.  Picric  acid  does  not  precipi- 
tate mucin,  and  is  therefore  a  valuable  con- 
firmatory test. 

(d]  Bodeker's  method.      Take   a   drachm   of  the   urine, 

acidulate  it  with  acetic  acid,  and  add  some  potas- 
sium ferrocyanide  drop  by  drop  till  a  clear  excess 
has  been  added.  If  during  the  addition  a  pre- 
cipitate forms,  albumin  is  to  be  suspected.  Mere 
traces  require  some  time  to  cause  the  cloud. 

(e]  To  estimate  the  albumin.     This  may  be  done  empirically  by  means 

of  an  albumino meter  (fig.  48).  Fill  to  u  with  the  urine  and  R 
with  the  precipitant  (picric  acid  10  grms.,  citric  acid  20 
grms.,  and  water  to  make  1000  c.c.).  Mix  by  inverting  the 
tube  several  times,  not  by  agitation,  and  set  aside  for  24  hours. 
The  height  of  the  precipitate,  as  indicated  by  the  graduations, 
represents  the  grains  of  albumin  per  thousand  c.c.  of  urine.  Be 
careful  to  read  the  height  of  the  precipitate  from  the  middle  of 
the  albuminous  surface.  If  the  urine  is  alkaline,  make  it  acid 
with  acetic  acid.  In  the  absence  of  such  a  convenient  appliance 
\ve  may  take  a  weighed  quantity  of  the  urine,  and  allow  it  to 


1. 


Fig  48. 


224  ANALYSIS   OF  DRUGS,   ETC. 

drop  into  boiling  water  acidulated  with  acetic  acid.  Collect  the 
precipitate  on  a  tared  filter,  wash  with  boiling  water,  dry  at 
100°  C.,  weigh,  and  deduct  the  weight  of  the  filter,  when  the 
balance  =  albumin  in  the  weight  of  urine  operated  upon. 

5.  Test  for  grape  sugar,  as  follows: — 

(a)  Moore's  test.     Acidulate  with  acetic  acid,  boil,  and  filter  out  any 

albumin  if  necessary.  Then  mix  the  filtrate  with  equal  parts  of 
liquor  potasses  and  heat  to  boiling,  when  ordinary  urine  will  turn 
brownish  red,  but  saccharine  urine  will  become  dark  brown  or 
black. 

(b)  B.cttger's   test  (modified   by  Nylander).     Dissolve    2*5    grms.   of 

pure  bismuth  oxynitrate  (free  especially  from  silver)  and  4 
grms.  of  Rochelle  salt  in  100  grins,  of  8  per  cent,  solution 
of  sodium  hydrate,  and  preserve  for  use.  To  use  this  reagent 
i  c.c.  of  urine  is  added  to  jo  c.c.,  and  the  whole  boiled  gently 
for  some  time,  when  if  even  only  traces  of  sugar  be  present 
the  mixture  becomes  black. 

(c)  Failing's  test.     Render  the  urine  alkaline  with  potassium  hydrate, 

and  filter  to  remove  any  phosphates,  etc.,  which  may  pre- 
cipitate. Boil  the  filtrate  with  Fehling's  solution  of  copper  (see 
page  130),  and  if  a  precipitate  should  form  sugar  is  present. 

(d)  To  estimate   the  sugar.     This  is  best   done  by  taking   10  grms. 

of  the  urine  and  diluting  it  with  water  to  100  c.c.  Place  this 
solution  in  a  burette,  and  run  it  gradually  into  10  c.c.  of  Pavy's 
or  Fehling's  solution,  kept  boiling  in  a  flask  as  directed  under 
the  Volumetric  Analysis  of  Sugar,  page  130.  The  number  of 
c.c.  of  urine  used  will  contain  '005  grm.  of  grape  sugar  if 
Pavy's  solution,  or  '05  grm.  if  Fehling's,  was  used,  and  then 

100  x  '005   /T1       x         100  x  'ex;  /T,  ,  ,.     x 

^-  (Pavy).  or  ^(tehling)  ••  sugar   in   the  10 

c.c.  used  c.c.  used 

grms.  of  urine  taken. 

(£)  Estimation  of  sugar  by  fermentation.  Take  I  grm.  of  com- 
mercial compressed  yeast;  shake  thoroughly  in  the  graduated 
test  tube  with  10  c.c.  of  the  urine  to  be  examined.  Then  pour 
the  mixture  into  the  bulb  of  the  saccharometer  (shown  in  fig.  49, 
page  218).  By  inclining  the  apparatus  the  mixture  will  easily 
flow  into  the  cylinder,  thereby  forcing  out  the  air.  Owing  to 
the  atmospheric  pressure  the  fluid  does  not  flow  back,  but 
remains  there.  The  apparatus  is  to  be  left  undisturbed  for  20 
to  24  hours  in  a  room  of  ordinary  temperature.  If  the  urine 
contains  sugar,  alcoholic  fermentation  begins  in  about  20  to 
30  minutes.  The  evolved  carbonic  acid  gas  gathers  at  the  top 
of  the  cylinder,  forcing  the  fluid  back  into  the  bulb.  On  the 
following  day  the  upper  part  of  the  cylinder  is  filled  with 
carbonic  acid  gas.  The  changed  level  of  the  fluid  in  the 
cylinder  shows  that  the  reaction  has  taken  place,  and  indicates 
by  the  numbers — to  which  it  corresponds — the  approximate 
quantity  of  sugar  present.  If  the  urine  contains  more  than 
I  per  cent,  of  sugar,  then  it  must  be  diluted  with  water  before 
being  tested.  Diabetic  urines  of  straw  colour  and  a  specific 

fravity  of  1018 — 1022  may  be  diluted  twice;  of  1022 — 1028, 
ve  times  ;  1028 — 1038,  ten  times.     The  original  (not  diluted) 
urine  contains,  in  proportion  to  the  dilution,  two,  five,  or  ten 
times  more  sugar  than  the  diluted  urine. 


ANALYSIS   OF  URINE. 


22$ 


Fig.  49. 


6.  Test  for  bile,  as  follows  :  — 

(a)  Oliver's    test.      Dissolve    2    grms.    of    flesh    peptone,    '25    grm. 

of  salicylic  acid,  and    2  c.c.   of  33  per  cent,   acetic  acid  in 

enough  water   to  yield  200  c.c.  of  pro- 

duct.    The  solution  should  be  rendered 

perfectly  brilliant  by  passing  it  through 

frozen  filtering  paper.     The  urine,  which 

should   be   very   clear,    is   diluted   to   a 

specific    gravity   of   roo8.      One   cubic 

centimetre  of  this  is  added  to  3  c.c.  of 

Oliver's    reagent.      An    opalescence    at 

once  appears,  which  will  be  found  to  be 

more   or  less  distinct   according  to   the 

quantity  of  bile  salts   present.     Keller's 

contact   method   can  be  advantageously 

employed  for  applying  the  test. 

(b)  Gmeliris  test  for  bile  pigments.      Place  a  drachm  of  nitric  acid  in 

a  test  tube,  and  cautiously  pour  upon  it  an  equal  volume  of  the 
urine.  In  the  presence  of  bile  a  play  of  colours  from  green 
to  violet,  blue,  and  red  will  be  observed  where  the  liquids  touch. 

(c)  Pettenkofer  's  test  for  biliary  acids.     Mix  equal  parts  of  urine  and 

sulphuric  acid,  add  one  drop  of  saturated  syrup,  and  apply  a 
gentle  heat.     If  biliary  acids  be  present,  the  colour  will  change 
from  cherry-red  to  deep  purple. 
Note.  —  Bilious  urine  is  usually  of  a  brownish-green  colour. 

7.  Test  for  urea,  as  follows  :  — 

(a)  Separate  any  albumin  (as  directed  in  Moore's  test)  if  necessary, 

and  evaporate  an  ounce  of  the  urine  to  a  syrupy  consistence  on 
the  water  bath.  When  cold  add  nitric  acid,  drop  by  drop,  till 
crystals  of  nitrate  of  urea  cease  to  deposit. 

(b)  Estimation  of  urea.     This  is  performed  by  the  hypobromite  process 

already  given  at  page  135.    Normal  urine  contains  2  to  3  per  cent. 

8.  Test  for  uric  acid  by  mixing  one  ounce  of  the  urine  with  one  drachm  of 

hydrochloric  acid  in  a  beaker,  and  set  aside 
for  some  hours.  The  uric  acid  will  be  de- 
posited in  reddish-brown  crystals,  which 
may,  if  desired,  be  weighed  and  proved  by 
the  murexid  test.  Normal  urine  contains 
3  to  7  parts  per  thousand. 

A  volumetric  method  is  also  used  which  is 
based  on  the  known  fact  that  argentic  urate 
is  insoluble  in  ammonia,  but  dissolves 
in  nitric  acid.  The  solutions  required 
are:  —  i.  "T^j-  ammonium  thiocyanate  "  ; 
dissolve  about  8  grms.  of  ammonium 
thiocyanate  in  a  litre  of  water,  and  check 
with  £y  argentic  nitrate  solution;  dilute 
it  for  use  with  nine  volumes  of  water. 

2.  Dissolve    5    grms.    of   argentic    nitrate 
in    100   c.c.    of   distilled   water,    and    add 
ammonia  until  the  solution  becomes  clear. 

3.  Dilute  70  per  cent,  nitric  acid  with  two 
volumes  of  distilled  water,  boil,  to  destroy 


Fig. 
P,  linen 


.  50.-  Extraneous  Matters  often  seen  in  the  lower    Oxides    of  nitrogen^  and   preSCFVC 
Urine.    A,  silk  ;  B,  cotton  ;  c,  wool  ;         f  ,  r   T    i  A 

en;  E,  feather;  F,  mycelium;  c,  cork    from    the    action    of  light.      4.    A   saturated 


IS 


226  ANALYSIS  OF  DRUGS,   ETC. 

solution  of  ferric  alum.  5.  Strong  solution  of  ammonia.  The  following  is  a 
description  of  the  process : — Place  25  c.c.  of  urine  in  a  beaker  with  i  grm. 
of  sodium  bicarbonate.  Add  2  or  3  c.c.  of  strong  ammonia,  and  then  i  or 
2  c.c.  (or  an  excess)  of  the  ammoniated  silver  solution.  A  special  procedure 
is  necessary  in  order  to  collect  the  precipitate,  as  follows  : — Fill  a  glass 
funnel  to  about  one  third  with  broken  glass,  and  cover  this  with  a  bed  of  good 
asbestos  to  about  a  quarter  of  an  inch  deep.  This  is  best  done  by  shaking 
the  latter  in  a  flask  with  water  until  the  fibres  are  thoroughly  separated, 
and  then  pouring  .the  emulsion  so  prepared  in  separate  portions  on  to  the 
broken  glass.  On  account  of  the  nature  of  the  precipitate  and  of  the  filter, 
it  is  necessary  to  use  a  Bunsen  water  pump  in  order  to  suck  the  liquid 
through.  Having  thus  collected  the  precipitate,  wash  it  with  distilled  water 
until  the  filtrate  ceases  to  become  opalescent  with  a  solution  of  NaCl.  Now 
dissolve  the  precipitate  by  washing  it  through  the  filter  into  a  beaker,  with 
a  few  cubic  centimetres  of  the  special  nitric  acid.  Estimate  the  silver  by 
Volhard's  method  thus  : — Add  to  the  liquid  in  the  beaker  a  few  drops  of  the 
ferric  alum  solution  to  act  as  an  indicator,  and  from  a  burette  carefully  drop 
in  y^-  ammonium  thiocyanate  solution  until  a  permanent  red  colour  appears. 
The  number  of  c.c.  used,  multiplied  by  "00168,  gives  the  amount  of  uric  acid 
in  the  25  c.c.  of  urine.  One  milligramme  may  be  added  to  this  amount  as  an 
allowance  for  average  loss,  and  the  whole  multiplied  by  4  gives  the  percentage 
of  uric  acid  in  the  urine.  The  sodium  bicarbonate  is  added  in  the  early  part  of 
the  process,  to  prevent  decomposition  of  the  argentic  urate,  which  would  other- 
wise occur.  This  method  has,  however,  been  lately  stated  to  be  unreliable. 

9.  Test  for  phosphates,  as  follows  : — 

(a)  Add  to  one  ounce  of  the  urine  a  slight  excess  of  ammonium 
hydrate,  and  boil.  Ca3(PO4)2  and  MgNH4PO4  will  both  be 
precipitated,  and  the  precipitate,  if  more  than  a  distinct  cloud, 
should  be  filtered  out,  dissolved  in  HC1,  and  analysed  by  the 
ordinary  process  already  given  for  phosphates. 

(J?)  After  filtering  out  the  earthy  phosphates  as  above,  alkaline  phos- 
phates may  be  tested  for  by  adding  magnesia  mixture  to  the 
filtrate,  and  getting  the  usual  precipitate  of  MgNH4PO4  after 
standing  some  hours  in  a  cold  place. 

(c)  Estimation  of  phosphates.  This  is  done  by  the  volumetric  process 
with  uranic  nitrate,  already  described  at  page  131.  Normal 
urine  contains  2  to  3  parts  P2O5  per  thousand. 

10.  Test  for  sulphates,  as  follows  : — 

Acidulate  a  little  of  the  urine  with  HC1,  warm,  and  add  excess  of 
BaCl2.  If  the  precipitate  appear  too  copious,  estimate  as  usual, 
using  50  c.c.  urine  (see  page  132).  Normal  urine  contains 
1*5  to  3  parts  SOs  per  thousand. 

11.  Test  for  chlorides,  as  follows  : — 

Acidulate  a  little  of  the  urine  with  HNOs,  and  add  excess  of  argentic 
nitrate.  If  the  precipitate  thus  produced  looks  very  large,  a 
weighed  quantity  of  the  urine  should  be  taken,  and  the  chlorides 
estimated  by  Volhard's  method  (see  page  118).  Normal  urine 
contains  5  to  10  parts  sodium  chloride  per  thousand. 

12.  Blood  is  best  seen  under  the  microscope;  but  urine  containing  it  has 
always  a  very  characteristic  smoky  appearance.     A  test  for  blood  is  "to  add 
tincture  of  guaiacum  and  ethereal  solution  of  hydrogen  peroxide,  which  pro- 
duce a  sapphire  blue ;  but  such  colour  of  itself  should  not  be  taken  as  positive 
proof  without  the  blood  discs  beings  also  visible  under  the  microscope, 


ANALYSTS  OF  URINARY  CALCULI. 


227 


DIVISION   III,     ANALYSIS    OF    URINARY    CALCULI, 

The  following  table  will  show  at  a  glance  the  compositions  and  methods  of 
proving  the  various  calculi. 

1.  Calculi,  fragments  of  which,  heated  to  redness  on  platinum, 
entirely  burn  away. 


NAME. 


PHYSICAL  CHARACTERS. 


CHEMICAL  CHARACTERS. 


Urid  acid,  C5N4H,O3. 


Ammonium  urate. 


Cystine, 


Xanthin,  C3II4N4O2. 


Brownish-red  ;  smooth 
or  tuberculated  ; 
concentric  laminae 
(common). 

Clay-coloured  ;  usually 
smooth,  and  rarely 
with  fine  concentric 
laminae  (uncommon). 

Brownish-yellow, 
semi-transparent  and 
crystalline  (very  un- 
common). 

Pale  polished  brown 
surface  (very  un- 
common). 


Insoluble  in  water  ;  soluble  in  KHO 
by  heat,  but  evolves  no  NH3 ;  dis- 
solves with  effervescence  in  HNOV 
and  the  residue  on  evaporating  the 
solution  is  red  and  gives  the  murexid 
test. 

Soluble  in  hot  water  ;  soluble  in 
heated  KHO,  evolving  NH3.  Be- 
haves with  HNO3  like  uric  acid. 

Insoluble  in  H2O,  alcohol,  and  ether. 
Soluble  in  NH4HO,  and  depositing, 
when  allowed  to  evaporate  spon- 
taneously, hexagonal  plates.  When 
heated,  gives  off  odour  of  CS2. 

Soluble  in  KHO  ;  soluble  in  HNO3 
without  effervescence,  and  the  solu- 
tion leaves  on  evaporation  a  deep 
yellow  residue. 


2.  Calculi,  fragments  of  which,  heated  to  redness  on  platinum, 
do  not  burn  away, 


NAME. 


PHYSICAL  CHARACTERS. 


CHEMICAL  CHARACTERS. 


Calcium  oxalate, 

mulberry        calculus, 

CaCA- 


Tricalcium  phosphate, 
bone-earth  calculus, 
Ca3(P04)2. 


Magnesium   ammonium 
phosphate,  triple 

phosphate       calculus, 
MgNH,PO4. 

Mixed     phosphates     of 
Ca,    Mg,    and    NII4, 

fusible  calculus. 


Deep  brown,  hard,  and 
rough  ;  thick  layers 
(common). 


Pale  brown,  with  regu- 
lar laminae  (uncom- 
mon). 


White,  brittle,  crys- 
talline, with  an  un- 
even and  not  usually 
laminated  surface 
(uncommon). 

White,  and  rarely 
laminated. 


Insoluble  in  acetic  acid,  but  soluble, 
without  effervescence,  in  HC1 ; 
heated  to  redness,  it  is  converted 
into  CaCO3,  which  dissolves  with 
effervescence  in  acetic  acid,  and  the 
solution  gives  a  white  precipitate 
with  (NH4)2C.,O4.  Heated  strongly 
before  the  blow-pipe,  CaO  remains, 
which,  when  moistened,  is  alkaline 
to  test-paper. 

Infusible  before  the  blow-pipe,  and 
residue,  when  moistened,  is  not  al- 
kaline. Soluble  in  HC1,  and  the 
solution  gives  a  gelatinous  precipi- 
tate with  excess  of  NH4HO. 

Fusible  with  difficulty  before  the 
blow-pipe,  evolving  NH3,  and  re- 
sidue not  alkaline.  Soluble  in  HC1, 
and  solution  gives  white  crystalline 
precipitate  with  NH4HO. 

Readily  fusible  before  the  blow-pipe. 
Soluble  in  acetic  acid,  and  solution 
gives  a  white  precipitate  with 
(NH4)2C2O4,  and  the  filtrate  from 
that  precipitate  gives  a  white  pre- 
cipitate with  excess  of  NH4HO. 


CHAPTER    XII. 

THE  TAKING  OF  MELTING,  SOLIDIFYING,  AND  BOIL- 
ING POINTS,  POLARISATION  ANALYSIS,  SPECTRUM 
ANAL  YSIS,  AND  THE  ANAL  YSIS  OF  GASES. 


DIVISION    I.      THE    TAKING    OF    MELTING,    SOLIDIFYING,    AND 

BOILING  POINTS, 

(1)  Melting   Points,      Many   methods   have    been    from    time    to    time 
proposed,  but  the  following  will  be   found  to  be   sufficiently  good   for  all 
ordinary  purposes,  and  is,  moreover,   the  method  officially  adopted  in  the 
Pharmacopoeia. 

A  piece  of  narrow  glass  tube  is  softened  in  the  gas  flame  and  drawn  out,  so 
as  to  give  it  a  long  thin  end  with  a  capillary  bore  of  about  i  millimetre.  The 
substance  is  melted,  and  a  little  of  it  is  sucked  up  into  this  capillary  tube  and 
allowed  to  solidify  therein.  The  tube,  having  been  sealed  at  the  lower  end, 
is  then  tied  to  a  delicate  thermometer  so  that  the  substance  is  near  the 
middle  of  the  bulb,  and  the  thermometer  with  the  attached  tube  should  be 
immersed  in  a  suitable  liquid,  contained  in  a  beaker  placed  over  a  small  lamp 
flame.  Water  is  suitable  for  substances  melting  below  212°  F.  (100  C), 
sulphuric  acid,  hard  paraffin,  or  glycerine  for  substances  melting  at  higher 
temperatures.  The  liquid  should  be  continually  stirred  by  means  of  a  glass 
ring  moved  up  and  down  till  the  substance  is  seen  to  melt.  The  temperature 
is  noted,  the  tube  cooled  till  the  substance  solidifies,  and  the  operation  then 
repeated.  The  latter  reading  of  the  thermometer  should  be  taken  as  the 
melting  point.  To  obtain  accurate  results,  the  whole  of  the  mercury  column 
of  the  thermometer  should  be  immersed  in  the  heated  liquid ;  but  as  this  is 
seldom  practicable,  the  mean  temperature  of  the  emergent  column — that  is, 
of  that  portion  above  the  surface  of  the  heated  liquid — should  be  ascertained 
and  the  necessary  correction  applied.  To  obtain  the  mean  temperature  of 
the  emergent  column,  a  small  thermometer  is  fixed  by  india-rubber  bands  in 
such  a  position  that  its  bulb  is  about  the  middle  of  the  emergent  column. 
The  corrected  temperature  may  be  calculated  with  approximate  accuracy  from 
the  formula : — 

Corrected  Temperature  =  T  -f  '000143  (T  —  t)  N,  in  which 
T  =  observed,  i.e.  uncorrected,  temperature ; 
t    =  mean  temperature  of  the  emergent  column  ; 
N  =  the  length  of  the  emergent  column  in  scale  degrees. 

(2)  Solidifying  Points.     It  frequently  happens,  especially  in  solid  fats,  that 
this  is  a  more  constant  factor  than  the  melting  point.     We  heat  the  substance 
to  a  temperature  of  about  ten  degrees  above  its  melting  point,  and  place  it  in 
a  glass  cylinder  surrounded  by  cotton-wool.     We  then  stir   slowly  with  a 
delicate  thermometer,  and,  as  the  liquid  cools,  the  temperature  regularly  falls, 
until  a  moment  arrives  when,  after  a  slight  pause,  the  thermometer  shows  a 


ANALYSIS  BY  CIRCULAR  POLARISATION.  229 

sudden  rise  of  a  fraction  of  a  degree.     This  is  then  the  solidifying  point  of 
the  fat. 

(3)  Boiling  Points.  To  determine  the  boiling  point  of  a  substance,  the 
liquid  under  examination  should  be  placed  in  a  distilling  flask  having  a  side 
tube  for  conveying  the  vapour  to  a  condenser,  while  the  thermometer  passes 
through  a  cork  inserted  in  the  neck.  The  bulb  of  the  thermometer  should 
be  near  to,  but  not  immersed  in,  the  liquid,  and  the  whole  of  the  thread  of 
mercury  should  be  surrounded  by  the  vapour ;  the  temperature  is  read  off  as 
soon  as  the  liquid  is  distilling  freely.  With  certain  substances  (such  as  melted 
hydrous  chloral)  which  do  not  boil  without  "bumping,"  it  is  necessary  to 
introduce  a  few  fragments  of  broken  glass  or  recently  ignited  clay  tobacco 
pipe.  All  boiling  points  are  supposed  to  be  taken  under  a  normal  barometric 
pressure  (760  mm.,  or  29^  inches),  therefore  we  must  always  read  the  pressure 
for  the  day,  and  either  add  to  or  deduct  from  the  observed  boiling  point  fi°  C. 
for  every  27  mm.  of  barometric  variation. 

DIVISION  II.    ANALYSIS  BY  CIRCULAR  POLARISATION. 
THE  SACCHAROMETER. 

Crystals  which  do  not  belong  to  the  regular  system  (notably  calc-spar) 
possess  the  power  of  double  refraction.  That  is  to  say,  when  a  ray  of  light 
falls  upon  them,  it  is  divided  into  two  rays,  one  of  which  follows  the  ordinary 
rule  of  refraction,  while  the  other  takes  a  totally  different  course ;  and  the  two 
rays  are  called  respectively  the  "  ordinary  "  and  the  "  extraordinary  "  ray. 
The  most  convenient  polarising  medium  is  what  is  called  a  "  Nicol's  prism." 
It  is  composed  of  a  crystal  of  calc-spar  cut  into  two  portions  in  the  direction 
of  its  axis,  and  the  two  parts  thus  obtained  cemented  together  with  Canada 
balsam.  When  a  beam  of  light  enters  the  prism,  it  is  doubly  refracted  by  the 
first  portion  of  the  crystal,  and  the  extraordinary  ray  only  passes  through  the 
second  portion  to  the  eye  of  the  observer ;  while  the  ordinary  ray  is  com- 
pletely reflected  away  by  the  layer  of  Canada  balsam,  and  so  lost  to  view. 
When  this  extraordinary  ray  is  examined,  it  is  found  to  possess  peculiar 
properties,  such  as  showing  colour  in  transparent  bodies  which  are  usually 
colourless.  This  is  accounted  for  by  believing  that  it  has  become  polarised 
— i.e.,  that  all  its  vibrations  have  been  reduced  to  the  same  plane.  If  the 
polarised  light  thus  obtained  be  examined  by  means  of  another  Nicol's  prism, 
it  will  be  found  that,  when  the  two  prisms  are  placed  with  the  principal 
sections  parallel  to  each  other,  the  ray  will  pass  freely ;  but  if  the  second 
prism,  called  the  analyser,  be  then  turned  round,  so  that  its  chief  section  is 
at  right  angles  to  that  of  the  first,  the  polarised  ray  will  in  turn  be  entirely 
reflected  from  the  layer  of  balsam,  and  no  light  will  now  reach  the  observer's 
eye.  This  holds  good  so  long  as  nothing  intervenes  between  the  two  prisms  ; 
but  it  has  been  found  that  certain  bodies,  such  as  quartz,  possess  the  power, 
when  interposed  between  the  prisms,  of  giving  a  colour  instead  of  darkness, 
owing  to  their  possessing  the  power  of  twisting  the  polarised  ray  from  its 
original  plane.  Such  substances  are  said  to  possess  the  power  of  circular 
polarisation,  either  in  a  "right-handed"  or  "left-handed"  direction,  accord- 
ing as  it  is  necessary  to  turn  the  prism  either  to  the  right  or  left  from  its 
proper  position,  to  once  more  produce  complete  passage  of  the  colourless 
polarised  ray.  The  direction  of  the  rotation  is  indicated  by  the  use  of  arrows, 
thus  :  c?*o.  Cane  sugar,  grape  sugar,  dextrin,  maltose,  creasote,  camphor, 
turpentine  (American),  cinchonine,  castor  oil,  croton  oil,  and  lemon  oil,  rotate 
the  plane  of  the  polarised  ray  to  the  right ;  while  fruit  or  (invert)  sugar,  quinine, 
cinchonidine,  turpentine  (French),  and  many  essential  oils,  morphine,  etc., 
have  a  left-handed  rotation. 

There  are  two  varieties  of  quartz,  known  as  right-handed  and  left-handed, 


23o    MELTING,  ETC.,  POINTS;   ANALYSIS  OF  GASES,  ETC. 

one  of  which  rotates  the  plane  of  polarisation  to  the  right,  and  the  other  to 
the  left.  If  a  plate  of  quartz  i  millimetre  thick  be  placed  between  the  two 
"  Nicol's/'the  ray  of  polarised  light  is  rotated,  and,  instead  of  being  colourless, 
is  coloured,  changing  to  all  the  colours  of  the  spectrum  as  the  analyser  is 
turned,  until  it  once  more  becomes  colourless,  and  the  amount  that  the 
analyser  has  to  be  turned  (registered  by  a  pointer  on  the  degrees  of  the 
circle)  is  the  index  of  rotary  polarisation  possessed  by  the  quartz  either  in  a 
right  or  left-handed  direction.  If  the  turning  of  the  analyser  be  now  con- 
tinued, colour  will  again  show  itself,  but  this  time  it  will  be  the  colour 
complementary  to  that  at  first  produced.  Thus,  if  we  start  with  a  plate  of 
quartz  showing  red  between  the  uncrossed  prisms,  and  rotate,  we  shall  find 
that,  when  we  have  turned  through  an  angle  of  45°,  we  get  no  colour,  but 
after  that  we  begin  to  get  the  complementary  colour  green,  which  becomes 
most  intense  at  the  right  angle  of  90°,  when  the  prisms  are  crossed.  The 
polariscope  as  used  for  analysis  is  therefore  essentially  (a)  a  Nicol's  prism 
acting  as  a  polariser,  (b]  a  plate  of  quartz  usually  divided  down  the  centre, 
the  one  side  being  right-handed  and  the  other  left,  (c)  a  tube  to  contain  the 
solution,  (d)  another  "  Nicol "  capable  of  being  rotated,  and  having  a  pointer 
acting  on  degrees  of  the  circle  on  a  scale,  (e)  a  telescope  to  focus  the  line 
between  the  two  sides  of  the  quartz.  When  the  pointer  is  placed  at  zero, 
the  tube  filled  with  water,  and  the  line  focussed,  no  colour  is  seen  on  either 
side  of  it ;  but  if  a  solution,  say  of  sugar,  be  introduced,  colour  appears  on 
one  side  of  the  line  according  to  the  nature  of  the  sugar,  and  then  the 
distance  through  which  the  pointer  has  to  be  moved  round  the  graduated 
circle  to  get  both  sides  of  the  quartz  colourless  is  the  degree  of  rotary 
polarisation.  In  practice,  monochromatic  light  from  a  sodium  flame  is 
employed,  which  causes  a  dark  shadow,  instead  of  a  colour,  to  appear  when 
the  instrument  is  used,  so  enabling  colour-blind  persons  to  employ  it  without 
difficulty.  Another  reason  for  the  employment  of  a  definite  monochromatic 
light  lies  in  the  fact  that  the  rotating  power  of  bodies  alters  according  to  the 
ray  of  the  spectrum  used,  being  least  for  the  red  rays,  and  increasing  till  it 
reaches  its  highest  point  at  the  violet  end  of  the  spectrum.  Optical  deter- 
minations are  made  in  a  dark  room,  and  the  instrument  is  illuminated  by  a 
bead  of  fused  sodium  chloride  held  by  a  platinum  support  in  a  "Bunsen" 
flame.  Light  thus  obtained  corresponds  to  that  emitted  at  the  D  line  of  the 
solar  spectrum. 

Since  the  deviation  of  the  plane  of  polarisation  either  to  the  right  or  to 
the  left  of  the  zero  point  is  directly  proportional  to  the  length  of  the  column 
of  liquid,  it  is  important  that  the  observations  should  be  made  with  tubes  of 
a  definite  length,  such  as  100,  50,  or  25  mm.  The  selection  of  the  length 
of  the  tube  to  be  employee!  is,  however,  usually  dependent  upon  the  depth 
of  colour  of  the  liquid  and  the  extent  of  its  optical  rotation.  The  rotatory 
power  of  an  optically  active,  liquid  substance,  observed  with  sodium  light, 
and  referred  to  the  ideal  density  i,  and  in  a  tube  having  a  length  of  i  deci- 
metre (100  mm.),  is  designated  as  its  specific  rotatory  poiver.  This  is  usually 
expressed  by  the  term  [a]D.  Since,  however,  not  only  the  density  of  an 
optically  active  liquid,  but  also  its  rotation,  is  influenced  by  the  temperature, 
the  specific  rotation  varies  with  the  latter.  In  stating  the  specific  rotation, 
it  is  therefore  necessary  to  indicate  at  what  temperature  the  rotation  and  the 
density  of  the  liquid  have  been  determined.  But  for  the  same  temperature 
the  specific  rotation  of  a  pure,  optically  active  liquid  is  always  a  constant 
number.  To  use  the  instrument  we  make  a  solution  of  the  body  to  be 
examined  of  a  definite  percentage  strength  by  dissolving  a  certain  number 
of  grammes  in  100  c.c.  of  a  solvent.  We  then  fill  the  tube,  observe  the 
degree  of  rotation  produced,  and  from  that  we  calculate  the  absolute  angle 


SPECTR UM  ANAL YSIS.  231 

of  rotation  for  the  sodium  light  (always  expressed  as  [a]D)  by  the  following 
formula  and  factors  : — 

I.   For  liquid  substances         [a]D  =-^ 

L  X  d 

TT      T-  i    i.-  r       i'j        /     r    i  IOOOO    X    d 

II.   r  or  solutions  or  solids    |    [ajn  = 


or    I    [>]D  = 


L  X  p  X  d 
10000  X  a 


L  x  c 

a  =  the  angle  of  rotation  of  the  liquid  or  solid  observed  with  sodium  light 
L  =  the  length  of  the  tube  in  millimetres, 
d  =  the  density  or  specific  gravity  of  the  active  liquid, 
p  =  the  amount  of  active  substance  in  100  parts  by  weight  of  the  solution, 
c  =  the  number  of  grammes  of  active  substance  in  100  c.c.  of  the  solution. 
If  the  absolute  angle  thus  found  coincides  with  that  obtained  from  the  same  substance  in  a 
state  of  purity,  then  the  article  under  examination  is  pure  ;  but  if  not,  then  a  simple  percentage 
calculation  gives  the  impurity. 

Thus  the  [a]D  of  pure  cane  sugar  =  66*5 .    A  sample  examined  as  above  gave  an  [a]o  =  65-5, 

Then :     5  ^  *  IO°  =  per  cent,  of  real  sugar  present  in  the  sample. 

UO  '^ 

DIVISION  III.     SPECTRUM  ANALYSIS 

When  a  ray  of  sunlight  is  allowed  to  pass  through  a  prism,  it  is  deflected 
and  dispersed  into  a  number  of  rays  differing  in  their  degree  of  refrangibility. 
When  these  rays,  as  they  pass  from  the  prism,  are  caused  to  fall  upon  a  white 
surface,  they  are  observed  to  have  a  marked  difference  in  colour.  The  image 
so  produced  is  called  a  spectrum ;  and  when  sunlight  is  thus  treated  it  is 
found  to  give  a  spectrum  consisting  of  the  following  colours — viz.,  violet,  indigo, 
blue,  green,  yellow,  orange,  and  red.  The  violet  end  of  the  spectrum,  owing 
to  its  greater  refrangibility,  is  always  the  nearer  to  the  base  or  broad  end  of 
the  prism.  By  this  means  of  separating  the  rays  of  light  we  are  able  to  ascertain 
the  peculiar  properties  of  each  of  the  colours  which  go  to  compose  it,  and 
we  find  that  the  chemical  activity  of  light  resides  chiefly  in  the  most  highly 
refrangible  rays  just  outside  the  violet  end  of  the  visible  spectrum,  which 
are  called  the  actinic  rays ;  while,  on  the  other  hand,  the  heat  transmitted 
by  the  sun  is  most  felt  at  the  opposite  or  red  end  of  the  spectrum. 

Further  research  has  demonstrated  that,  if  we  substituted  the  light  emitted 
fiom  various  bodies  in  a  state  of  incandescence  to  the  action  of  a  prism,  the 
image  or  spectrum  produced  varied  in  each  case,  and  was,  moreover,  almost 
characteristic  of  the  particular  bodies  employed.  This  discovery  led  to  the 
invention  of  the  spectroscope,  which,  in  its  simplest  form,  consists  of  a 
metallic  diaphragm  with  a  narrow  slit,  through  which  a  lay  of  light  from  the 
burning  body  is  allowed  to  pass  and  is  condensed  by  a  lens  upon  a  prism 
of  glass,  or,  better  still,  a  triangular  bottle  of  thin  glass  filled  with  disulphide 
of  carbon.  At  the  opposite  side  of  the  prism  is  a  short  telescope,  so  arranged 
that  an  observer,  looking  through  it,  sees  the  spectrum  or  image  produced 
by  the  light  after  passing  through  the  prism.  This  telescope  works  upon  a 
graduated  scale,  by  which  its  position  for  viewing  any  particular  line  observed 
can  be  noted. 

When  ordinary  solar  light  is  examined  through  the  spectroscope,  a  number 
of  dark  lines  are  found  crossing  the  image  at  certain  fixed  points.  They  are 
called  "  Fraunhofer's  lines,"  and  their  position  is  characteristic  of  sunlight 
It  has  been  proved  that  such  lines  are  only  formed  when  the  source  of  light 
contains  volatile  substances,  as  we  find  that  the  light  emitted  by  a  non-volatile 
heated  body  gives  a  continuous  image,  devoid  of  lines.  If,  for  example,  a 
platinum  wire  be  heated  to  a  high  temperature  in  a  Bunsen  burner,  and  tne 
light  thus  produced  be  examined,  no  lines  will  be  visible ;  but  if  the  wire  be 


232    MELTING,  ETC.,  POINTS;  ANALYSIS  Of  GASES,  ETC. 


now  tipped  with  a  fragment  of  sodium  chloride,  and  once  more  ignited,  a 
bright  line  will  suddenly  appear  in  the  yellow  of  the  spectrum,  and  in  so 
dazzling  a  manner  as  to  render  the  whole  of  the  rest  of  the  image  almost 
invisible.  In  carrying  out  this  system  of  analysis,  therefore,  it  is  only  necessary 
to  procure  a  perfectly  clean  piece  of  platinum  wire,  with  one  end  bent  into 
the  form  of  a  loop,  and  place  a  Bunsen  gas  burner  in  such  a  position  that  the 
rays  from  anything  heated  in  it  will  pass  into  the  spectroscope.  The  wire  is 
then  to  be  moistened  with  a  little  hydrochloric  acid,  and,  having  been  dipped 
in  the  substance  to  be  examined,  is  to  be  held  in  the  hottest  portion  of  the 
Bunsen  flame,  and  its  spectrum  simultaneously  observed  through  the  spectro- 
scope, noting  carefully  the  colour,  number,  and  position  on  the  scale,  of  the 
bright  lines  produced.  When  thus  examined  we  find  that  potassium  exhibits 
one  bright  line  in  the  red,  and  one  in  the  blue ;  lithium,  one  bright  line  in 
the  yellow,  and  one  more  brilliant  in  the  red;  strontium,  one  blue,  one 
orange,  and  six  red  lines  ;  barium,  a  number  of  lines  chiefly  green  and  yellow ; 
calcium,  three  distinct  bright  yellow  lines,  one  within  green,  and  some  broad 
but  indistinct  ones  in  the  orange  and  red;  and  lastly,  sodium,  the  single 
bright  yellow  line  already  mentioned. 

The  student  must  commence  with  the  examination  of  pure  salts,  carefully 
noting  for  reference  the  position  of  the  index  of  the  telescope  on  the  scale 
where  each  characteristic  line  is  found.  When  it  is  desired  to  examine  any 
mixture,  the  telescope  index  is  brought  to  the  required  position  and  the 
substance  is  examined  :  if  the  proper  line  is  seen,  then  the  element  searched 
for  is  present ;  if  not,  it  is  absent.  If  we  examine  ordinary  light  which  has 
been  made  to  pass  through  solutions  of  various  coloured  bodies,  we  obtain 
dark  bands  analogous  to  the  lines  of  Fraunhofer.  These  are  called  absorption 
spectra,  and  are  very  useful  in  the  detection  of  soluble 
colouring-matters.  A  solution  of  blood,  for  example, 
shows  characteristic  bands  in  the  green  of  the  spectrum. 
All  this  is  a  matter  of  special  study,  and  to  go  farther 
into  it  would  be  beyond  the  scope  of  this  volume. 


DIVISION  IV.     THE  ANALYSIS  OF   GASES. 

This  operation  is  conducted  by  measuring  a  volume 
of  the  mixed  gas  under  definite  conditions  of  temperature 
and  pressure,  then  exposing  it  to  the  action  of  some 
substance  having  the  power  of  absorbing  some  one  con- 
stituent of  the  mixture,  and  again  measuring  the  gas  left. 
By  seeing  that  the  inside  of  the  measuring  tube  is  always 
kept  moist  the  question  of  tension  of  aqueous  vapour  is 
equalised  all  through  the  experiment,  and  as  many  ab- 
sorbents as  may  be  necessary  are  employed  in  turn 
Many  of  the  gas-measuring  appliances  are  large,  costly, 
and  require  to  be  kept  in  special  rooms  devoted  to  the 
purpose.  Hempel  has,  however,  devised  a  gas-measuring 
apparatus  which  is  reasonable  in  price,  and  yet  is  capable 
of  measuring  gas  volumes  with  very  fair  accuracy.  It 
consists  essentially  of  a  vessel  for  measuring  volumes 
of  gas— known  as  a  Gas  Burette— and  a  number  of  other 
vessels— called  Gas  Pipettes— in  which  the  necessary 
absorptions  are  carried  out. 

The  Gas  Burette  (fig.  51)  is  an  arrangement  similar 
to  the  Nitrometer  already  fully  described  at  page  133, 
and  is  composed  of  two  tubes,  A  and  u.  The  tube  B  is 


THE  ANALYSIS  OF  GASES. 


233 


graduated  in  cubic  centimetres,  and  has  a  capacity  of  100  c.c.  It  is  closed 
at  c  by  a  piece  of  india-rubber  tube  and  a  pinch-cock,  and  at  d  is  connected 
by  a  long  flexible  tube  with  A.  To  measure  off  a  volume  of  gas  insoluble 
in  water,  the  two  tubes  are  completely  filled  with  water,  c  is  closed  and  A  is 
partially  emptied.  Connection  is  now  made  at  c  with  the  vessel  containing 
the  gas,  c  is  opened,  the  gas  flows  into  B  and  an  equal  volume  of  water  runs 


Fig. 


Fig.  53- 


into  A  (which  is  placed  on  a  lower  level  if  necessary),  aad  after  adjusting 
the  level  of  the  water  in  the  two  tubes  the  volume  is  read  off. 

Of  the  Gas  Pipettes  there  are  three  forms.  Fig.  52  is  a  single  pipette, 
and  has  two  bulbs,  E  and  F,  connected  by  a  tube,  t.  The  bulb  E  terminates 
in  a  capillary  tube  /£,  by  which  connection  is  made  with  the  gas  burette. 
In  using  the  pipette  E  is  completely  filled  with  the  reagent  intended  to  act 
on  the  gas.  The  gas  burette  is  closely  connected  with  k  by  means  of  a  small 


black  rubber  tube,  and  by  raising  A  and  opening  c  the  gas  is  forced  into  E, 
part  of  the  reagent  into  F.  After  the  absorption — which  may  be  quickened 
by  shaking — is  completed,  the  gas  is  again  allowed  to  flow  back  into  B,  c  is 
closed,  the  water  levels  are  adjusted,  and  the  volume  is  read  off  as  before. 

Fig.  53  is  a  modification  with  an  opening  at  /  closed  by  a  cork.  It  is 
adapted  for  use  with  solid  reagents,  e.g.,  moist  phosphorus  for  the  absorption 
of  oxygen. 


234    MELTING,  ETC.,  POINTS;   ANALYSIS  OF  GASES,  ETC. 


Fig.  54  is  a  compound  absorption  pipette,  and  is  for  use  with  solutions 
which  require  to  be  preserved  from  the  action  of  the  oxygen  of  the  air, 
such  as  alkaline  solution  of  potassium  pyrogallate  for  absorbing  oxygen,  or 
ammoniacal  cuprous  chloride  for  absorbing  CO.  The  bulb  E  is  filled  with 
the  solution,  the  bulb  G  with  distilled  water.  By  means  of  the  water  in  G  the 
solution  is  exposed  to  the  action  of  only  a  small  quantity  of  air  in  F,  which  is 
quickly  deprived  of  its  oxygen,  and  thus  the  absorbing  power  of  the  solution 
remains  unimpaired. 

To  perform  an  analysis  100  c.c.  of  gas  are  measured  off  in  the  burette,  this 
volume  being  chosen  so  that  the  result  of  each  absorption  may  represent, 
without  calculation,  the  percentage  of  volume  of  the  absorbed  gas  contained 
in  the  mixture.  As  many  pipettes  are  prepared  and  furnished  with  the 
necessary  reagents  as  there  are  constituents  in  the  gas.  The  gas  is  then 
passed  into  each  of  these,  allowed  to  remain  a  sufficient  time  for  the  absorption 
to  take  place,  again  collected  in  the  burette,  and  the  change  of  volume  noted. 


55. 


The  chief  absorbents  employed  in  gas  analysis  are  as  follows,  it  being 
understood  that  it  is  necessary  to  employ  them  in  such  an  order  as  shall  be 
suitable  to  the  particular  mixture  of  gases  under  analysis  : — 

A.  Strong  solution  of  potassium  hydrate  absorbs  CO2. 

J?.   i  vol.  of  25  per  cent,  solution  of  pyrogallic  acid  +  6  vols.  60  pei 

cent,  solution  of  KHO  absorbs  O2  (after  removal  of  any  gas 

absorbed  by  KHO  alone). 

C.  Moist  phosphorus  absorbs  oxygen,  but  not  CO2. 

D.  Concentrated  solution  of  cuprous  chloride  in  dilute  hydrochloric 

acid  absorbs  CO  (after  removal  of  CO  and  O2  with  alkaline 
pyrogallate). 

E.  Ammoniacal   solution    of   cuprous    chloride   absorbs    C2H2,    after 

removal  of  CO,  CO.2,  and  O. 

fr.  Palladium  black  absorbs  hydrogen,  but  not  CH4.  The  palladium 
black  is  contained  in  a  (J  tube,  one  limb  of  which  is 
connected  to  the  burette,  the  other  to  a  simple  absorption 
pipette  filled  with  water.  The  gas  is  passed  backwards 
and  forwards  over  the  palladium  several  times,  and  complete 
absorption  takes  place. 

G.  A  solution  of  sulphuric  anhydride  in  strong  sulphuric  acid,  or 
solution  of  bromine,  absorbs  C2H4,  and  the  other  gaseous 
hydrocarbons  of  the  series  CJi^,  and  of  CnH2n.2. 


THE  ANALYSIS   OF  GASES. 


235 


H.  The  addition  of  an  excess  of  pure  oxygen,  and  absorption  with 
alkaline  pyrogallate,  will  remove  NO,  together  with  the  excess  of 
oxygen  used.  NO  is  also  readily  absorbed  by  solution  of 
FeSO4. 

/.  Marsh  gas  and  nitrogen  are  left  to  be  estimated  by  difference. 
They  may  be  separated  by  adding  more  than  double  the  volume 
of  pure  oxygen,  measuring  the  total  volume,  and  passing  the 
mixture  into  an  explosion  pipette  (fig.  55),  where  it  is  ignited  by  an 
electric  spark  between  two  platinum  terminals  fused  into  the 
upper  part  of  E.  The  marsh  gas  then  forms  CO2  and  H2O,  and 
the  resulting  gas  having  been  treated  in  the  KHO  pipette  to 


Fig.  56- 

remove  the  CO2,  and  then  remeasured,  \  of  the  total  loss  in 
volume  represents  the  CH4  present.  Lastly,  the  excess  of  O2 
having  been  removed  by  alkaline  pyrogallate,  the  remainder 
isN2. 

/.  If  the  mixture  should  contain  HC1,  HBr,  HI,  SO2,  H2S,  and  NH3, 
all  of  which  are  soluble  in  water,  they  are  previously  dissolved 
out  thereby  in  a  special  apparatus  (fig.  56),  and  the  solution  so 
obtained  is  treated  by  methods  of  gravimetric  and  ordinary 
volumetric  analysis. 

Full  details  of  the  analysis  of  gases,  beyond  the  scope  of  the  present  work, 
will  be  found  in  Button's  "  Volumetric  Analysis." 


APPENDIX. 


LIST    OF    THE    ATOMIC    WEIGHTS     OF    THE    CHIEF 
ELEMENTS  REFERRED   TO  IN   THIS  MANUAL. 

NAME.  ATOMIC  WEIGHT. 

Aluminium      .         .         .         .         .         .         .         .         .  26*90 

Antimony 119*00 

Arsenium          .........  74'4O 

Barium    ..........  136*40 

Bismuth  ..........  206*90 

Boron 10*90 

Bromine 79'36 

Calcium  ..........  39'8o 

Carbon    ..........  11*91 

Cerium I39'2O 

Chlorine  .         .         .         .         .         .         .         .         .  35' 18 

Chromium        .........  51*70 

Copper 63*10 

Gold I957o 

Hydrogen        .         .         .         . 1*00 

Iodine 125*90 

Iron 55'5o 

Lead 205*35 

Lithium   ..........         6*98 

Magnesium      .........  24*18 

Manganese      .........  54'6o 

Mercury 198*50 

Nitrogen I3'93 

Oxygen 15*88 

Phosphorus 30*77 

Platinum 193'3O 

Potassium 38*86 

Silver 107*12 

Sodium 22*88 

Sulphur 31*83 

Tin ,  118*10 

Zinc 64*90 

236 


INDEX. 


Absorbents  in  gas  analysis,  234. 
Absorption,  pipettes,  233. 

Spectra,  232. 
Acetanilide,  84,  88. 
Acetates,  47. 
Acetic  acid,  47. 
Acetic  ether,  87. 
Acidimetry,  115. 
Acid  radicals,  detection  of,  29, 

75- 
Gravimetric  estimation  of, 

I5I 

Aconite  and   preps.,  assay  of, 

196. 

Adeps  lanae,  90. 
Air  bath,  140 

Air,  sanitary  analysis  of,  174. 
Albumin,  222. 
Albuminoid  ammonia,  171. 
Alcohol,  estimationof,  inspirits, 

etc.,  178. 

Table  of  percentages  of ,  179. 
Tests  for— 
Amyl,  87. 
Ethyl,  88. 
Methyl,  88. 
Alcoholic  bodies — 
Assay  of,  219. 
Estimation  of,  219. 
Aldehyds — 

Estimation  of,  114,  218. 
Alkalies,  organic  salts  of,  esti- 
mation of,  112. 
Alkalimetry,  109. 
Alkaline  course,  59. 

Carbonates,  estimation  of, 

112. 

Hydroxides     and     borax, 

estimation  of,  in. 
Alkaloidal  residues,  titration  of, 

195- 

Alkaloidal  strength  of  scale  pre- 
parations, 187. 
Alkaloids — 

Cinchona,  separation  of,  86. 
Detection  of,  84  to  87. 
Estimation  of,  186. 
Mydriatic,  196. 
Table  of  reactions  of,  facing 

p.  87. 

Tests  for,  84. 
Allyl-isothiocyanate,   assay  of, 

222. 

Almond  oil  testing,  210. 
Aloin,  90. 
Aluminium,  20. 

Gravimetric  estimation  of, 

148. 
Ammonia,  135. 

Albuminoid,  171. 

1'Ytv,  170. 
Ammoniacum,  194. 


Ammonium,  27. 

Gravimetric  estimation  of, 

IS1- 

Amyl  alcohol,  87. 
Amyl  nitrite,  87,  134. 
Analysis — 

Air,   sanitary  analysis  of, 
174. 

Balsams,  196. 

Bread,  180. 

Butter,  178. 

By  direct  oxidation,  124. 

By  immiscible  sol  vents,  1 86. 

Coffee,  182. 

Colorimetric,  136. 

Colored  sweets,  182. 

Drugs,  184. 

Essential  oils,  215. 

Flour,  1 80. 

Food,  175. 

Gases ,  H  em  pel"  s  a  ppar  atus, 
232. 

Gravimetric,  142. 

Gum  resins,  206. 

Milk,  175. 

Mineral,  of  water,  157. 

Mustard,  181. 

Nitrometer,  by  the,  133. 

Oils  and  fats,  208. 

Organic,  ultimate,  160. 

Pepper,  181. 

Polariscopic,  229. 

Qualitative,  i  to  93. 

Quantitative,  94  to  end. 

Scale  preparations,  91. 

Soap,  215. 

Spectrum,  231. 

Starch,  131. 

Urine,  222. 

Urinary  calculi,  227. 

Vinegar,  182. 

Volumetric,  104. 

Water,  167. 

Waxes,  212. 

Analytical  factors,  use  of,  142. 
Anion,  7. 
Anode,  6. 

Antifebrin,  tests  for,  88. 
Antimonic  acid,  46. 
Antimony,  16. 

Estimation  of,  146. 
Antipyrin,  tests  for,  90. 
Apomorphine,  85. 
Apparatus,  106,  160. 
Argentic  nitrate,  standard  solu- 
tion of,  116. 
Arseniates,  45. 

Estimation  of,  155. 
Arsenic,  15. 

Estimation  of,  146. 
Arsenic  acid,  45. 
Arsenious  acid,  44. 

Estimation  of,  120, 


Arsenites,  44. 
Asafetida,  206. 
Ash  of— 

Filters,  139. 

Organic  bodies,  141. 
Assay,  alkaloidal  of — 

Aconite  and  preps. ,  196. 

Belladonna    and     preps. , 

196  to  199. 
Cinchona,  190. 
Coca  and  preps. ,  199. 
Colchicum,  187. 
Conium  and  preps. ,  189. 
Guarana  and  preps. ,  192. 
Hydrastis  and  preps. ,  192. 
Hyoscyamus   and    preps., 

197  to  199. 

Ipecac  and  preps. ,  201. 
Nux  vomica  and    preps., 

201. 
Physostigma    and    preps., 

204. 
Pilocarpus     and      preps. , 

204. 

Opium  and  preps.,  193. 
Scopola  and  preps. ,  197  to 

199. 
Stramonium    and    preps. , 

197  to  199. 

Scale  preparations,  187. 
Atropine,  85. 


Balance,  94. 

Balsams,  analysis  of,  207. 

Peru,  207. 

Tolu,  207. 

Storax,  207. 
Barium,  24. 

Chloride,  standard  solution 
of,  132. 

Estimation  of,  149. 
Barks,  cinchona,  assay  of,  190. 
Beer,    alcoholic     strength    of, 

178. 

Bees'  wax,  analysis  of,  212. 
Belladonna  and   preps.,  assay 

of,  196  to  199. 
Benzoates,  51. 
Benzoic  acid,  51. 
Benzoin,  207. 
Benzin  (petroleum),  87. 
Benzol,  87. 

Bichromate  of  potassium,  stan- 
dard solution  of,  128. 
Bile  (urine),  225. 

Ox,  91. 
Bismuth,  14. 

Estimation  of,  145. 
Blood  (urine),  226. 
Bodeker'smethod,  223. 


238 


INDEX. 


Boettger's  test,  224. 
Boiling-point,  5. 

Taking  the,  229. 
Borntes,  37. 
Borax  beads,  60. 
Boric  acid,  37. 

Estimation  of,  156. 
Boyle's  law,  100. 
Bread,  analysis  of,  180. 
Bromates,  31. 
Bromides,  30. 

Estimation    of,    117,     151, 

154. 

Estimation  of,  in  presence 
of  chlorides,  117. 

Separation  of,  53. 
Bromine,  30. 

Estimation  of,  121. 

Standard  solution  of,  123. 
Brucine,  85. 
Bunsen  burner,  9. 
Bunsen's  battery,  6. 
Butter,  analysis  of,  178. 


Cacao  butter  testing,  211. 
Cadmium,  15. 

Estimation  of,  144. 
Caffeine,  85. 
Calcium,  25. 

Estimation  of,  149. 
Calculi,   urinary,   analysis    of, 

227. 

Cane  sugar,  90. 
Carbolates,  51. 
Carbolic  acid,  51,  57. 
Carbon,  36. 

Dioxide  in  air,  175. 

Estimation  of,  161. 
Carbonates,  36. 

Estimation       of       (gravi- 
metric), 155 

Estimation        of        (volu- 
metric), 112. 

Estimation  of  soluble,  134. 
Carbonic  acid,  36. 
Castor  oil  testing,  210. 
Cerium,  20. 
Charcoal,  use  of,  8. 
Charles's  law,  100. 
Chemical  processes,  i. 
Chloral  hydrate,  tests  for,  90. 
Chlorates,  30. 
Chlorides,  29,  53. 

Gravimetric  estimation  of, 

I5I- 

Volumetric   estimation  of, 

117. 
Volumetric  estimation  of, 

with  bromides,  117. 
With   bromides,  detection 

of.  53- 
With  iodides,  detection  of, 

Chlorine,  29. 

Available,    estimation    of, 

122. 
Estimation  of,  in  solution, 

122. 

In  organic  analysis,  166. 
Chloroform,  tests  for,  87. 
Chromates,  45. 
Chromic  acid,  45. 


Chromium,  ai. 

Estimation  of,  148. 
Chrysarobin,  tests  for,  90. 
Cinchona  and  preps. ,  assay  of, 

190. 

Cinchonidine,  86. 
Cinchonine,  86. 
Citrates,  50. 
Citric  acid,  50. 
Clark's  process,  172. 
Coca  and  preps. ,  assay  of,  199, 

200. 
Cobalt,  23. 

Estimation  of,  147. 
Cocaine,  85. 
Codeine,  85. 

Cod  liver  oil  testing,  210. 
Coefficients  for  analysis,  137. 
Coffee,  analysis,  182. 
Colchicum   and   preps.,    assay 

of,  187,  189. 
Colloids,  6. 

Colorimetric  analysis,  136. 
Conium  and  preps.,  assay  of, 

189. 
Copper,  14. 

Estimation  of,  144. 

Fehling's  standard  solution 

of,  129. 

Cotton  oil  testing,  211. 
Creasote,  88. 
Croton  oil  testing,  211. 
Crucible,  Rose's,  5. 
Crum  process,  168. 
Crystallisation,  5. 
Cupellation,  4. 
Cyanates,  41. 
Cyanic  acid,  41. 
Cyanides,  40. 

Estimation  of,  gravimetric, 

ISI- 

Volumetric,  116. 
Cyanogen,  40. 
Cyanuric  acid,  41. 


Decantation,  3. 
Density,  vapour,  101. 
Detection  of — 
Alkaloids,  84. 
Bromine,  hydrobromic  acid 

and  bromides,  30. 
Bromides   in    presence  of 

iodides,  53. 
Carbolic  acid  in  presence  of 

salicylic  acid,  57. 
Chlorides   in    presence  of 

bromides,  53. 
Chlorides   in    presence   of 

iodides,  53. 
Chlorine, hydrochloric  acid, 

and  chlorides,  29. 
Cyanides    in    presence    of 

ferro-  and  ferri-cyanides, 

56. 
Formate    in     presence    of 

fixed  organic  acids,  56. 
Inorganic  acids,  78. 
lodate  in  an  iodide,  54. 
Metals,  10. 

In  any  simple  salt,  61. 

In  complex  mixtures,  65. 


Detection  of  (contd.}— 

Nitrate  in  presence  of 
iodide,  55. 

Nitric  acid  (free)  in  pre- 
sence of  nitrate,  55. 

Nitrite  in  presence  of  a 
nitrate,  55. 

Organic  acids,  80. 

Organic  bodies  used  in 
medicine,  87. 

Phosphate  in  presence  of 
calcium,  barium,  stron- 
tium, manganese,  mag- 
nesium, or  iron,  56. 

Soluble  sulphide  in  pre- 
sence of  sulphite  and 
sulphate,  54. 

Sugar,  75. 
Dialysis,  5. 
Digestive  ferments,  analysis  of, 

T93- 

Distillation,  4. 
Dragendorff  s  tables,  86. 
Drugs,  analysis,  184. 
Dumas'  process,  165. 


Ebullition,  5. 

Elaterin,  tests  for,  98. 

Electrolysis,  6. 

Electrolyte,  7. 

Essential  oils,  analysis  of,  215 

to  222. 

Esters,  assay  of,  217. 
Estimation  of — 
Acids,  114. 
Albumin,  222. 
Alcoholic  bodies  in  essen- 
tial oils,  219. 
Aldehyds  in  essential  oils, 

218. 

Alkaline  carbonates,  112. 
,,        hydroxides,  in. 
Alkaloids,  186  et  seg. 
Allyl-isothiocyanate,  222. 
Aluminium,  148. 
Ammonia     (Nesslerising), 

136. 

Ammonium,  151. 
Antimony,  120,  146. 
Arseniates,  155. 
Arsenic,  146. 
Arsenious  acid,  120. 
Ash  of  filters,  139. 

,,    of  organic  bodies,  141. 
Barium,  149. 
Bismuth,  145. 
Borax,  in. 

Boric  acid  in  borates,  156. 
Bromides,  117,  154. 
Bromine,  121. 
Cadmium,  144. 
Calcium,  149. 
Carbon  and  hydrogen,  161. 
Carbonates,  155. 
Carbon  dioxide  in  air,  174. 
Chlorides,  116,  151. 

, ,          in  the  presence  of 
bromides,  117. 
Chlorine,  available,  122. 
,,         free,  121. 
,,         in       organic 
bodies,  166. 


INDEX. 


239 


Estimation  ot(contd.) — 

Chlorine  in  water  analysis, 

168. 

Chromium,  148. 
Cobalt,  147. 
Copper,  144. 

,,        and   iron,   minute 

traces  of,  136. 
Esters  in  essential  oils,  217. 
Extracts,      alkaloidal 

strength  of,  187  et  scq. 
Fatty  acids  in  soap,  215. 
Ferric  and  ferrous  salts, 

122,   128. 

Gold,  145. 

Gravimetric     (of    metals), 

138. 

Haloid  salts,  116,  119. 
Hydrocyanic  acid,  117. 
Hydrogen  peroxide,  128, 

I35- 

Hypophosphites,  126. 

Iodides,  116,  151. 

,,  in  presence  of 
bromide  and 
chloride,  117. 

Iodine,  free,  121. 

Iron,  125,  127,  148. 

Ketones,  in  essential  oils, 
219. 

Lead,  113,  143. 

Magnesium,  149. 

Manganese,  149. 

Mercury,  143. 

Metals  as  oxalates,  128. 

Mineral  oil  in  fats,  212. 

Moisture,  141. 

Morphine  in  opium,  194. 

Nickel,  147. 

Nitric  acid  in  nitrates,  134. 

Nitrites,  152. 

,,        m  water  analysis, 

137. 
Nitrogen,  164. 

,,         in  water  analysis, 
1 68. 

Nitrous  ether,  133. 
Olcic  acid,  210. 
Organic  matter  in  air,  174 
salts    of   alkalies, 

112. 

Oxalic  acid  and  oxalates, 

109,  128,  156. 
Peroxides,  128. 
Pepsin,  206. 
Phenol,  124. 
Phenols   in   essential   oils, 

218. 
Phosphates,  153. 

In  artificial  manures,  154. 
Phosphoric  acid,  116,  131, 

*S3- 
Phosphorus      in      organic 

bodies,  166. 
Platinum,  145. 
Potassium,  150. 

,,          andsodium,i5i. 
Resin  in  soap,  215. 
Rosin  oil  in  fats,  212. 
Scale  preparations,  182. 
Silicic  acid,  157. 
Silver,  142. 
Sodium,  150. 

,,        nitrite,  137. 


Estimation  of  (contd.) — 

Soluble    carbonates,    112, 

134- 

Soluble  haloid  salts,  116. 

Sugar,  estimation  of,  131. 
,,      in  urine,  224. 

Starch,  131. 

Sulphates,  131,  152. 

Sulphides,  152. 

Sulphites,  1 20. 

Sulphur  in  organic  bodies, 
166. 

Sulphurous  acid,  120. 

Tartaric  acid,  156. 

Thiosulphates,  121. 

Tin,  145. 

Urea  in  urine,  135. 

Zinc,  148. 
Ether,  acetic,  87. 

Nitrous  (estimation),  133. 
Ethyl  alcohol,  test  for,  88. 

Nitrite,  134. 
Ethylsulphates,  47. 
Evaporation,  5. 
Examination,  preliminary,  58 
Extraction,  2. 

Extracts,   estimation   of,  alka- 
loidal strength  of,  187  etseq. 


Factors,    analytical     (use    of), 

142. 

Fats,  analysis  of,  208. 
Fatty  acids,  estimation  of,  215. 
Fehling's  solution,  129. 

Test  in  urine,  224. 
Fel  Bovinum,  91. 
Ferments,  digestive,  206. 
Ferric  and  ferrous  salts  (estima- 
tion), 122,  128. 
Ferricyanides,  42. 
Ferro-      from      ferri-cyanides, 

separation,  56. 
Ferrocyanides,  41. 
Filters,  preparation  of,  138. 

Ash,  estimation  of  weight 

of,  139- 
Filtration,  3. 
Flame,  oxidising,  7. 

Reducing,  7. 

Tests,  60. 
Flour,  170. 
Fluorides,  29. 
Food  analysis,  175. 
Formic  acid  and  formates,  46 
Fraunhofer's  lines,  223. 
Free  acids  in  oils,  212. 
Fulminic  acid,  41. 
Fusion,  4. 


G 

Gallic  acid,  52. 

Gas  burette,  232. 

Gaseous  impurities  (testing  for, 

in  air),  174. 
Gases,  sp.  gr. ,  100. 
Analysis  of,  232. 
Correction  of  volume  of,  for 
temperature    and    pres- 
sure, 100. 


Gelatine,  tests  for,  91. 
Glucose,  89. 
Glusidum,  tests  for,  89. 
Glycerine,  88. 
Gmelin's  test,  225. 
Gold,  17. 

Estimation  of,  145. 
Grape  sugar,  90. 
Gravill's  test,  134. 
Gravimetric  estimations,  138. 

Acid  radicals,  151. 

Metals,  142. 
Gravity,  specific,  of— 

Essential  oils,  215. 

Gases,  100. 

Liquids,  96. 

Milk,  175. 

Oil  and  fats,  208. 

Solids,  98. 

Waxes,  212. 
Group  reagents,  10. 
Guaiacum,  206. 
Guarana  and  preps. ,  assay  of, 

192. 
Gum  resins,  206. 

H 

Haloid  salts,  estimation  of,  119, 

IS2- 

Hardness,  Clark's  process,  172. 
Hempel's  apparatus,  232. 
Homatropine,  85. 
Hubl's  method,  209. 
Hydrastinine,  85. 
Hydrastis  and  preps. ,  assay  of, 

192. 

Hydriodic  acid,  31. 
Hydrobromic  acid,  30. 
Hydrochloric  acid,  29. 

Standard  solution  of,  no. 
Hydrocyanic  acid,  40,  117. 
Hydrofluoric  acid,  29. 
Hydrofluosilicic  acid,  38. 
Hydrogen,    estimation    of,    in 

organic  analysis,  161. 
Peroxide,     estimation    of, 

128,  135. 

Hydrosulphuric  acid,  33. 
Hydroxides,  32. 

Alkaline,  estimation  of,  1 1 1. 
Hyoscine,  85.  • 
Hyoscyamine,  85. 
Hyoscyamus  and  preps. ,  assay 

of,  197  to  19*9. 
Hypobromites,  31. 
Hypochlorites,  30. 
Hypophosphites,  42. 
Hyposulphites,  34. 


Igniting  precipitates,  140. 

Indicators,  105. 

Inorganic  acid  course,  78. 

lodates,  32. 

lodate  with  iodide,  detection  of, 

54- 
Iodides,  31,  35. 

Estimation  of,  117,  151. 

Estimation  of,  in  presence 
of  a  chloride  and  a  bro- 
mide, 152. 


240 


INDEX. 


Iodine,  31. 

Estimation  of,  121. 
Standard  solution  of,  120. 
lodoform,  tests  for,  91. 
Iron,  18. 

Gravimetric  estimation  of, 

148. 
Volumetric  estimation  of, 

by  bichromate,  128. 
Volumetric  estimation  of, 

by  permanganate,  127. 
Ipecac   and    preps.,  assay  of, 
201. 


Jalap,  assay  of,  206. 
Jalapin,  tests  for,  91. 


K 

Kathion,  7. 
Kathode,  6. 
Ketones,  assay  of,  219. 
Kipp's  apparatus,  9. 
Kjeldahl's  process,  166. 


Lactates,  48. 
Lactic  acid,  48. 
Lactose,  90. 
Lard  testing,  211. 

,,     oil  testing,  211. 
Laws — 

Boyle's,  100. 

Charles's,  100. 
Lead,  12. 

Estimation  of,  113,  143. 
Liebig's  condenser,  4. 
Linseed  oil  testing,  211. 
Lithium,  26. 
Lixiviation,  2. 

M 

Magnesium,  26. 

Estimation  of,  149. 
Malates,  49,  57. 
Malic  acid,  49. 
Manganates,  45. 
Manganese,  21. 

Estimation  of,  147. 
Manures,   estimation  of  phos- 
phates in,  154. 

Mayer's  standard  solution,  132. 
Measuring  and  weighing,  94. 
Meconates,  51. 
Meconic  acid,  51. 
Melting  points,  228. 
Mercuricum,  13. 
Mercurosum,  12. 
Mercury,  estimation  of,  143. 
Metals,  detection  of,  10. 

Gravimetric  estimation  of, 
142. 

In  complex  mixtures,  65. 

Present  in  a  simple  salt,  61. 

Separation  of,  into  groups. 
10,  64,  66;  Hamilton's 
table,  74. 

Tables  for  detection  of,  62. 


Metaphosphoric  acid  and  salts, 

43- 
Method,  Meyer's,  102. 

Pavy's,  130. 

Varrentrapp,  164. 

Vol  hard's,  119. 
Methyl  alcohol,  88. 
Methylated  spirit,  in  tinctures, 

207. 
Milk,  analysis  of,  175. 

Sour,  analysis  of,  177. 

Sugar,  detection  of,  90. 
Mineral     contents     of     water, 

analysis  of,  157. 
Mineral  oil  in  oils,  212. 
Moisture,  estimation  of,  141. 
Moore's  test,  224. 
Morphine,  85. 
Murexid  test,  222. 
Mustard  analysis,  181. 
Myrrh,  207. 

N 

Naphtol,  89. 
Nesslerising,  136. 
Nickel,  23. 

Estimation  of,  147. 
Nitrates,  39,  55. 

Estimation    of,    by    nitro- 
meter, 134. 

Estimation  of,  gravimetric, 

152. 

Nitric  acid,  39. 
Nitrite  with  nitrate,   detection 

of.  55- 
Nitrites,  38. 

Estimation    of,    in    water 

analysis,  169. 
Nitrobenzene,  88. 
Nitrogen,  estimation  of,  164. 
Estimation    of,    in    water 

analysis,  168. 
Nitrometer,  use  of,  133. 
Analysis  by,  133. 
Nitrous  acid,  38. 
Nitrous  ether,  estimation  of,  133. 
Nux  vomica  and  preps.,  assay 
of,  201-203. 


Oils,  analysis  of,  208. 

Essential,  215. 

Free  acids  in,  212. 

Mineral  oils  in,  212. 

Qualitative  tests  for,  210. 

Rosin  oil  in,  212. 

Specific  heating  power  of, 

210. 

Oleates,  48. 
Oleic  acid,  48,  210. 
Olive  oil  testing,  211. 
Oliver's  test,  216. 
Opium  and  preps. ,  assay  of,  193. 
Organic  acid  course,  80. 

Analysis,  ultimate,  160. 

Matter  in  air,  175. 

Matter  in  water,  171. 
Organic  bodies  used  in  medicine, 

detection  of,  87. 
Orthophosphates,  43. 
Orthophosphoric  acid,  43. 


Oxalates,  48. 

Estimation  of  metals  as,  1 19. 
Oxalic  acid,  48. 

Gravimetric  estimation  of, 
156. 

Standard  solution  of,  109. 
Ox  bile,  91. 
Oxidation,  7. 
Oxides,  33. 
Oxygen    consumed    in    water 

analysis,   171. 


Pancreatin,  206. 
Paraldehyd,  tests  for,  88. 
Pavy's  method,  130. 
Pepper  analysis,  181. 
Pepsin,  206. 
Perchlorates,  30. 
Periodates,  32. 
Permanganate    of    potassium, 

standard  solution  of,  126. 
Permanganates,  45. 
Pettenkofer's  test,  225. 
,  Phenacetin,  tests  for,  89. 
Phenazone,  tests  for,  90. 
Phenol  and  phenates,  51,  124. 
Phenolic  ethers,  assay  of,  218. 
Phenols,  assay  of,  218. 
Phosphates — 

Detection  of,  43,  56,  226. 

Estimation  of,  as  magne- 
sium pyrophosphate  and 
phosphomolybdate,  153, 

154. 
Estimation  of  soluble,  in  a 

manure,  155. 
Estimation   of  total,  in  a 

manure  or  soil,  154. 
Volumetric  estimation   of, 

*3*. 

Phosphites,  43. 
Phosphoric  acid,  43. 

Gravimetric  estimation  of, 

free,  153. 
Volumetric  estimation  of, 

116. 

Phosphorous  acid,  43. 
Phosphorus,   estimation   of,  in 

organic  analysis,  166. 
Physical  constants  of  essential 

oils,  215. 
Physostigma  and  preps.,  assay 

of,  204,  205. 
Physostigmine,  85. 
Picrotoxin,  tests  for,  89. 
Pilocarpus   and   preps.,   assay 

of,  204. 

Pilocarpine,  85. 
Platinum,  18. 

Estimation  of,  145. 
Podophyllin,  tests  for,  91. 
Podophyllum  resin,  207. 
Poisons    in    mixtures,    testing 

for,  92. 

Polarisation,  analysis  by,  229. 
Potassium,  27. 

Bichromate,   standard  so- 
lution of,  128. 
Estimation  of,  150. 
Estimation  of,  with  sodium, 


INDEX. 


241 


Potassium  (cont.} — 

Hydroxide,  standard  solu-    | 
tion  of,  114. 

Permanganate,     standard 
solution  of,  126. 

Thiocyanate,  standard  so- 
lution of,  119. 

Precipitates,  drying,  etc.,  140. 
Precipitation,  2. 
Preliminary  examination,  58. 

Process,  Clark's,  172. 

Crum's,  168. 

Dumas',  103,  165. 

Kjeldahl's,  166. 

Liebig's,  161. 

Reichert's,  178. 
Processes,  chemical,  i. 
Pyrogallic  acid,  52. 
Pyrology,  7. 

Pyrophosphoric  acid  and  salts, 
43- 


Qualitative  analysis- 
Detection   and   separation 

of  acid  radicals,  29. 
Detection  of  alkaloids,  84. 
Detection  of  certain  organic 
bodies  used  in  medicine, 
87. 

Detection  of  metals,  10. 
"Scale"     medicinal     pre- 
parations, 91. 
Detection  of  unknown  salts, 

58. 

Processes,  r. 
Quantitative  analysis- 
Separations,  157. 
Specific  gravity,  96. 
Standard  solutions,  104. 
Vapour  density,  101. 
Weighing  and  measuring, 

94- 

Quinidine,  86. 
Quinine,  86. 

,,         tests  for  purity,  191. 


Radicals,  acid,  29,  75. 

Gravimetric  estimation  of, 

IS1- 
Reagents,  10. 

Group  I.,  IT. 

Group  II.  Div.  A,  13. 

Group  II.  Div.  B,  15. 

Group  III.  Div.  A,  18. 

Group  III.  Div.  B,  21. 

Group  IV.,  24. 

Group  V. ,  26. 
Reduction,  7,  8. 
Reichert's  process,  168. 
Resin,  tests  for,  91. 
Resina,  207. 
Resorcin,  tests  for,  90. 
Rosin  oil  in  fats,  212. 


Saccharimeter,  229. 
Saccharine,  tests  for,  89. 
Soluble,  tests  for,  89. 


Salicine,  84. 
Salicylic  acid,  52. 
Salol,  89. 
Salts— 

Detection  of  alkaloid,  84, 
86. 

Detection  of  unknown,  58- 

83- 

Used    in     pharmacopceia, 

table  for  detection  of,  64. 

Volumetric    estimation    of 

various,  104-129. 
Sanitary  analysis  of  air,  174. 

,,  ,,  water,  167. 

Santonin,  tests  for,  89. 
Saponification  equivalent,  209. 
Scale  preparations,  qualitative 

analysis  of,  91. 
Alkaloidal  strength  of,  187. 
Scammony  resin,  207. 
Scopola  and  preps.,  assay  of, 

197  to  199. 
Separation — 

Arseniate  from  phosphate, 

56. 
Chlorates   from   chlorides, 

Chlorides,     iodides,     bro- 
mides from  nitrates,  55. 

Cinchona  alkaloids,  86. 

Cyanides  from  chlorides,  55. 

Ferro-  from  ferri-cyanides, 
56. 

Group  metals,  66,  74. 

Iodide  from  bromide  and 
chloride,  53. 

Metals  in  groups,  66. 

Oxalates,  tartrates.citrates, 
malates,  57. 

Quantitative,  157. 

Silica  from  all  other  acids, 
54-  . 

Sulphides,    sulphites,    and 
sulphates,  54. 

Thiosulphates    from     sul- 
phides, 54. 
Silica,  37,  54. 
Silicates,  37. 
Silicic  acid,  37. 

Anhydride,    separation  of, 

54- 

Estimation  of,  157. 
Silver,  n. 

Estimation  of,  142. 
Soap,  analysis  of,  215. 

Resin  in,  215. 
Sodium,  27. 

Estimation  of,  150. 
Estimation  of,  with  potas- 
sium, 151. 
Chloride,  standard  solution 

of,  1 1 8. 

Hydroxide,  standard  solu- 
tion of,  115. 

Nitrite,  estimation  of,  134. 
Thiosulphate,        standard 

solution  of,  121. 
Soil,  estimation  of  phosphates 

in,  154. 

Solubility  tables,  82. 
Solution,  T. 
Solutions — 

Preparation  of,  to  test  for 
acids,  77. 


Solutions  (contd.} — 

Preparation  of,  to  test  for 
metals,  6r,  65. 

Standard,  104. 
Soxhlet's  apparatus,  2. 
Specific  gravity,  96-103. 
Specific  gravity  of — 

Alcoholic  bodies,  178. 

Essential  oils,  215. 

Gases,  100. 

Liquids,  96. 

Milk,  175. 

Oils  and  fats,  208. 

Solid  bodies,  98. 

Urine,  222. 

Specific  gravity,  practical  appli- 
cations of,  99. 
Specific  heating  power  of  oils, 

210. 

Spectrum  analysis,  231. 
Spermatozoa,  220. 
Spirits,   alcoholic    strength   of, 
178. 

Table  for  percentages,  178. 
Standard  solutions — 

Argentic  nitrate,  116. 

Barium  chloride,  132. 

Bromine,  123. 

Copper,  Fehling's,  129. 

Hydrochloric  acid,  no. 

Iodine,  120. 

Mayer's,  for  alkaloids,  132. 

Oxalic  acid,  109. 

Phosphate,  131. 

Potassium  bichromate,  128. 

Potassium  hydroxide,  114. 

Potassium   permanganate, 
126. 

Soap,  172. 

Sodium  chloride,  118. 

Sodium  hydroxide,  115. 

Sulphuric  acid,  no. 

Thiocyanate,  119. 

Thiosulphate,  121. 

Uranic  nitrate,  131. 
'    Stannates,  46. 
Stannic  acid,  46. 
Starch  estimation,  131. 
Stearates,  48. 
Stearic  acid,  48. 
Stramoniun  and  preps.,   assay 

of,  197  to  199. 
Strength  of  alkaloidal  extracts, 

187. 

Strontium,  25. 
Strychnine,  85. 
Sublimation,  4. 
Succi nates,  49. 
Succinic  acid,  49. 
Sucrose,  89. 
Sugar  estimation,  131. 

In  urine,  224. 
Sugars,  tests  for,  90. 
Sulphates,  35. 

Estimation    of,    132,    152, 

212. 
Sulphides,  33,  54. 

Estimation  of,  152. 
Sulphides,   sulphites,    and  sul 
phates,  separation  of,  54. 
Sulphites,  35. 
Sulphocyanates,  41. 
Sul  phonal,  89. 
Sulphovinates,  47. 

16 


242 


INDEX. 


Sulphur,  33. 

Estimation  of,   in  organic 

analysis,  166. 

Sulphuretted     hydrogen,    pre- 
paration of,  9. 
Sulphuric  acid,  35. 

Standard  solution  of,  no. 
Sulphurous  acid,  35. 

Estimation  of,  120. 
Sweets,  analysis  of,  182. 
Sykes's  hydrometer,  97. 


Tables- 
Detection  of  the  metal  in  a 

simple  salt,  the  metals  as 

in  pharmacopoeia,  64. 
Detection  of  the  metal  in  a 

solution  containing  one 

base  only,  62. 
Distinction  between  gallic, 

tannic,     and    pyrogallic 

acids,  52. 

General  reactions  of  alka- 
loids, 86. 

Percentages  of  alcohol,  169. 
Separation  of  metals  into 

groups,  66. 
Solubility  of  salts,  82. 
Specific   gravity    of    milk, 

temperature    corrections 

for,  176 


Tannic  acid,  52. 
1'artaric  acid,  49,  156. 
Tartrates,  49. 
Testing  for  poisons,  92. 
Thiocyanates,  41. 
Thiosulphates,  34. 

Estimation  of,  121. 
Tin,  17. 

Estimation  of,  145. 
Tinctures — 

Methyl  alcohol  in,  207. 
Toxicological  analysis,  92. 


U 

Ultimate  organic  analysis,  160. 
Uranic  nitrate,  standard  solu- 
tion of,  131. 
Urea,  estimation  of,  134. 

Test  for,  225 
Uric  acid,  222. 

Urinary  calculi,  analysis  of,  227. 
Urine — Analysis  of,  222. 

Estimation  of  urea  in,  135. 


Valerianates,  47. 
Valerianic  acid,  47. 
Valuation  of  ferments,  206. 
Van  Babo's  apparatus,  9. 


Vaporisation,  5. 
Vapour,  specific  gravity  of,  101. 
Vapours,  density  of,  101, 
Varrentrapp's  method,  165. 

Ditto  modified,  164. 
Veratrine,  84. 

Vinegar,  sulphuric  acid  in,  182. 
Volhard's  method,  119. 
Volumetric  analysis,  104. 


W 

Washing  precipitates,  139. 

Water,  32. 

Mineral  analysis  of,  157. 

Oven,  140. 

Sanitary  analysis  of,  167. 
Waxes,  analysis  of,  212. 

Tests    for    the    chief   un- 
official, 214. 
Weighing,  94,  106. 

Precipitates,  140. 
Westphal  balance,  97. 
Wines,  alcoholic  strength  of, 

178. 
Wool-fat  testing,  211. 


Zinc,  22. 

Estimation  of,  148. 


Printed  by  Hasell,  Watson  <S>  Viney,  Ld,t  London  and  Aylesbury,  England 


Date  Due 


1 


. 

NQV  2  4 

1930 

^•LP    4 

1931 

APR   18 

932 

• 

$33 

, 

i 

D2840 
*  analyti 
•fh  .»  ed. 

w  24  i:- 


5 


^   y 


OL  LIBRARY 


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